No matter what you do, short of falling off the face of the earth,  BM is going to pitch a fit. She has held your SD as an emotional hostage for years and now is doing the same to you. Let her be mad, you do what makes sense for your happy relationship with SD.

Instead of making changes to appease an unappeasable BM, you need to come up with a plan and key people to monitor BM and remove her if and when necessary.  The bride needs to warn her mother she will be removed if she acts up. ( after telling her she is wanted there)  That is  how you handle an addict. Spell out the expectations and consequences. 
 

BM 's behavior is hers and hers alone. If she messes up the wedding day, that has nothing to do with you.  You all know what she is. Act accordingly based on reality, not a wishfilled fantasy.  

Watch your back, Angel.  BM sounds like a volatile loony and must be fiercely jealous of you.

She chose to behave this crazy way and use you as a scapegoat because thats what narcs do,, blame someone else as nothing is their fault. She was this crazy before you even were in tbe picture 

so at the wedding when the shitstorm happens and bio mum blames you and chucks a tantrum, thats on her. Ruining her daughter’s big day was more important than making it wonderful, thats how narcs are

I think of SD is old enough to get married, she's old enough to consider the potential consequences of having you involved and make her own decision. You aren't responsible for how BM behaves. It would likely hurt your SDs feelings if you decline to participate. I would take the suggestion above and appoint someone to covertly supervise/manage BM as best as possible and then go about your business enjoying the day with SD.

Oh, come on!  Are you really that much into, "Take the high road and feel sorry for yourself."  

I fully get that BMs will always rule the day, even those who are (former) drug addicted hos.  However, there is no way in h- you should be anything other than your husband's wife or SO at SD's wedding, and in this case, SD elected you to be Matron of Honor too.  So, go and be your husband's wife or SO, meaning you are by his side for the day just like every other husband and partner at this event, and fulfill your role as Matron of Honor.

I really cannot believe that you feel you are somehow shaming BM and SD by, more or less, just being there, as if you are supposed to feel ashamed of being married or SO to your DH.  If you had no problem having them call you mom, then you should have no problem being your DH's wife or SO at this event, AND have no problem being your SD's Matron of Honor too.  And, by the way, it is an Honor to be Matron of Honor.  

If you were going to get involved with DH and the kids to turn around and kiss BM's butt when she decides to make an appearance and act like she is the #1 woman in their life (a woman it sounds to me like they all pretty much despised way before you entered the picture), then you should have never gotten involved with any of them to begin with. 

Protecting kids from their parent's poor choices by offering to be a buffer (whether that be physical, emotional, or financial) rarely works. I'm not advocating for kids to get beaten by their parent, but I am advocating for letting a sinking ship sink itself.

SD will be in this toxic back-and-forth with BM for longer than she needs to be if you go in there and try to be the buffer for her. SD is an adult. She knows how her mother behaves. If you were going to have a conversation with her about this, it would be a better use of your time to talk through how SD can mitigate any meltdowns BM is likely to have. That could mean not giving her access to liquor, assigning someone as her personal bouncer, telling BM how things are going to be beforehand and letting BM make the decision if she wants to be involved, etc.

I get with kids the need to not alienate them from their parent, but this sounds like a situation where BM literally walked away from all her parenting responsibilities. She didn't visit, didn't pay CS, and didn't even talk to her kids except when she was high/drunk. She did her own damage.

Now, having said all of this, I DO think you jumped WAY too quickly into the "mom" deepend with kids who suffered the trauma of losing their mother while she's still alive. To you, it likely feels great that they call you mom and have really taken to you. BUT, that comes from a place of trauma and desperation for a mother-figure after theirs abandoned them. 

Did your DH put either child in therapy after BM left? It sounds like, in addition to BM leaving, they may have been exposed to her drug use and inebriated behavior. That takes a toll on young adults, and it's likely to all boil to the surface someday in very unexpected ways.

Instead of stepping in to replace BM, your DH needs to impress upon both of his children that they need to seek some professional help to deal with that trauma. They likely have anger at him, too, for not stepping in sooner. They also need to learn that it's okay to NOT have a loving, trusting, normal relationship with BM, not because of their own anger but because she has caused that rift in them.

If you want to actually help these young adults, you do need to step back on the mothering role and shove your DH into the forefront who can handle these issues with them. Yes, they're adults and don't have to listen to him, but he needs to acknowledge his own culpability in what happened AND encourage his kids to seek professional help to work through the feelings they have. You being so accepted so quickly is enough evidence that they haven't processed what happened - they just masked it.

I haven't read everyone else's post yet. (I'm at work) Quick question.. is it new that both parents walk their daughter down the aisle?? 
 

I have been to (no sarcasm) about 15 weddings the past 8 years. Never seen this. 

I'm sure you will get all the attention you think you have coming to you and so clearly enjoy. 

Honestly, it's really hard to take you seriously. Your flowery, dramatic, catastrophizing language and behaviour makes me think that you welcome the drama in your life, like you are doing posting here. You just keep going on and on and on and on about poor me, blah, blah, blah. It's really hard to read anymore. I find myself skipping over your posts. Just thought I'd throw that out there as to why people may be responding to you negatively. What do you think?

Did everyone loose their ability to read today?   Did you miss the description of BM???  She bailed on the skids.

7 years ago and following an affair and well documented drug problem, BM walked out on her 20 year marriage and her children. It was especially difficult on her then 13yo son. He all but erased his mother from his life. SD stayed in contact with her mom, often to her own detriment. Now living with her boyfriend,  BM indulged her drug and alcohol demons with little protest. As a result, she would get drunk and high before calling her daughter and either ranting at her for choosing to live with her father or going into illicit detail about how she had slept with every one of her daughter's  boyfriends. (I assure you, this is true and we have the emails and texts to prove it.) Naturally, my SD was heartbroken.  

You have all lost sight of this fact and twisted responses to something else. IMO    Once again I tell OP, expectations and boundaries need to be spelled out to BM on what is expected of her on that day and what will happen if she acts up.  She sounds unreliable and you had better prepare for her drama.  

OP your skids are lucky that their father found you.  They accepted you for the most part and its noble of you to consider how to make the day smoother for your SD.  Unfortunately, you are dealing with an addict and you can NOT treat them the same as a normal person.  You just can't.  There are step parents around here who have dealt with addicts for BM's or BDs..  It not easy to do.  Encourage your SD to stand up for her day, her future husband and life.  She will have to deal with her mother the rest of her life.  Now is a good time for her to put some limits on her mother.  

All this drama is so unnecessary, it sounds like both BM and you like drama. Weren't you throwing yourself on the ground in your previous blog being all upset about your kids' SM? Demanding SM doesn't show up at kids events. I get it BM is crazy but no need to amp Up the drama. You aren't even married to a guy yet and you already tangled up in a mess and drama with BM. You were dramatic as BM fighting with SM and now you are dramatic SM. No need for that 

Wedding Etiquette.  Usually I’m not a big fan of wedding etiquette, per se, since it usually seems to be used in whatever manner so as to inflict as much discomfort on dad’s wife as possible, BUT I’ve just gone through “The Everything Wedding Etiquette Book, 4th edition, by Holly Lefevre.  On the back it states, “Your essential guide to the modern wedding,” and mentions dealing with unhappy stepfamilies.  So, I had to at least glance through it, of course.

Have to say, I was at least somewhat impressed (and that’s saying a lot for me).  What impressed me the most is that when it came to stepfamilies and where people sit, she stated quite clearly to get permissions from all parties involved.  She stated this a couple of times.  So, NO, it us not automatically just whatever the bride and groom wants, so suck it up !#@$! SM.  Also, what I found interesting, is that she recommended not seating exes that closely together EVEN IF they get along.  Here are some good quotes:

“The basic principle of etiquette can be summed up simply as the idea of not offending, embarrassing or upsetting others.”  (Aside: That sure as H- wasn’t followed at my SD’s wedding!)  “You should always invite significant others of married guests, engaged couples, couples who live together, and those who are generally considered to be a couple.” 

This was advice to a groom that didn’t want to invite his stepfather: “To invite your mother without her husband would be awkward, rude and offense to your mother.  If you insist on excluding your stepfather, you should discuss it first with your mother.”  Parents are not considered members of the wedding party, contrary to popular belief.  “The head table is usually reserved for the members of the wedding party.  Parents usually sit at separate tables with their families.”  “Divorced parents should not be seated at the same table, no matter how well they get along.”   More on that below. . .

This is the author’s response to the question:  Should ex-spouses or ex-in-laws be invited?  The author’s response is basically No, but what I found more interesting is what she goes on to say:  “Even if you think your relationship has evolved to a certain level and you feel okay inviting your ex, you may feel differently later or when the day comes.  Additionally, it can be confusing if you have children together and awkward for many of the guests to see your “old” wife, for instance, at an event meant to ring in the new.”  I think this plays into what there has been a lot of discussion about lately, and that is that being friendly-friendly with the ex is not a good thing, as it causes confusion for the kids and can be awkward for many others.