It sounds like your DH is still connected to BM and hasn't completely committed to you. Does he watch his ex mother-in-law every Wed and Sun? If so, that is way beyond normal. You need to have a "come to Jesus" talk with DH and ask him who he wants to make happy - you or his ex?

The only kid DH should be discussing with BM is the youngest, and at his age it shouldn't have to be very often. DH should not be discipline the kid for BM. BM can deal with the adult kids on her own. DH needs to quit responding to her, although it doesn't sound like he is ready to do that.

You are not over reacting. I don't think you are reacting enough!

I'm not sure why DH even bothered divorcing BM, if he was going to stay this involved with her.

reason, presumably they had irreconcilable differences. You're the "upgrade." 

As you said, she has her family to hang out with during the holidays.

We were in a similar predicament for a while. I found out it was mostly due to "adult" SK's wanting BM (bowel movement) in the picture. It was very awkward, indeed, when we were at a gathering and he was seated between his ex and current wives. He held both our hands to say "grace." The conversation on the way home was interesting. She was persistently in our lives repeatedly. I drew the line in the sand and told DH to get her out of our lives. She was nasty and snarky, always reminiscing with me about how wonderful their lives together were, how they met, etc. I finally said "That's obviously why you're divorced. DH tells a very different story." 

For the record, they've been divorced for decades; longer than they were even married, but she never moved on, dated or married. She reminds me of a Tennessee Williams Play (Streetcar Named Desire, and The Glass Menagerie, where the southern belle gets caught in a time warp and never moves forward.)

It can be done, but know it's probably because SK's are pushing for it. These "kids" no matter their ages always want to see "mommy and daddy" together. SD, in her 40's messaged her dad once telling him how happy she was that since BM was attending our function because "...we can finally be together as a family." What? How delusional is that?

This situation is way out of hand.  No way would I put up with any of that.  Your DH is acting as if he is still married to someone else.  Going over to discipline for her, babysitting her mom, the adult SKs are not kids and he no longer needs to discuss them with her.  I would refuse to attend any more holidays with her present and if he chooses her over you, leave.  Graduations, Weddings, one time events for SKs fine, anything else is a no way!!!

Curious Georgette is not a stepparent and has never been in a stepfamily:

BM is not the problem here - your husband is.  If he was willing to shut her down, this wouldn't be a problem.  Unfortunately, it doesn't seem like he was ready for a new relationship since he's still overly involved in his old one.  I don't think there's anything wrong in requesting/demanding changes. No reasonable person would be willing to put up with this situation. 

Your Mil is an adult.  She can do what she wants.  You can attend or stay home.  Your DH may think your approach to co-parenting is not what he wants.   You guys will have to work it out

The only event I attend with bm is a skid wedding or funeral.

This would bother any normal person. I would feel disrespected if my husband was always around his ex like that. He has maintained a decent relationship with her mother and father, but there is a line that doesn't get crossed because I am his wife. If your husband wants to maintain a relationship with his ex, he should probably let you go.

You are not over reacting.

You are not overreacting at all- and although it's a huge step to just divorce someone, I wouldn't say you would be wrong to be considering it, either.  Although 15 is still young to a point, all of your children are older and past the tender ages of truly being a "child." 

We have BM in our lives, too, but not to the degree you have.  My partners' family is still in touch with her a lot- my partners' Mom even gave me a bag of old wedding, prom, etc. photos of my partner and his ex together and told me not to dare throw them away!! They are in the attic, but it still peeves me off.  Yes, his children may want them one day- but give them to bio mom, or keep them yourself until the kids are older. 

My partner and BM still talk and text everyday, and share two children together.  It sucks and definitely stirs up feelings of insecurity and jealousy.  But, if any of us say we don't experience those feelings at some point, we are lying to ourselves.  If we have to be at a function together (for the step kids), we suck it up and deal with it, but it also hurts to see family going up and hugging her and saying they love her, how beautiful she is.  His family (nieces and nephews) still only call me by my first name, but still refer to her as "Aunt."  Ugh.

So, just wanted to tell you I sympathize with you, and it sounds like yours is a little bit more involved than my situation.  I also don't think I read you have children together, so that's a huge plus if you are thinking that this is for the birds and you'd like to move on with life, and someone that has a little less baggage that doesn't include a not-so-ex ex wife.

He'll no would I put up this. One good thing I can say about the bio mum in our life is she doesn't contact SO unless it's an emergency or when he texts her to ask about the girls and the days he has them and that's only to let her know he's on the bus. 
I mean the kids are 18 and 20, they are adults so I think the BM needs to chill out with the discipline, I thought when your kids are that age that's when co parents kind of grow more distant because your kids are adults, it's not like the co parenting at the age of when they were younger so yeah it's a bit weird he's running to her all the time. 

I could have written your post.  I have been on this crazy merry go round that never stops for 15 years.  The skids are all grown but BM continues to want to be part of DH's family.  The phone calls and texts from her are minimal these days (finally!) however she still continues to attend his family's functions therefore I don't go and I am conflicted by my own decision.  I have no advise to give you other than to say that you are not alone. 

The bottom line is BM needs to move on and blend with her own family not her ex's.  As I have mentioned in many posts prior I get a long great with my ex-husband and his family.  So does my husband for that matter.  Through the years I was invited to many things including holidays.  I never went.  I get along great with my ex-husbands second wife and now his third.  However when he was married to his second wife when my son was little and she was trying to create a relationship with his family she didn't need me around.  This was her family now, I would never interfere with that.  Any normal sane person would see that.  

Any BM that is still trying to hang around her ex's holidays is clearly not that there for the turkey.  She is there because she is trying to interfere in her ex's life and marriage.  Any normal person would see that.  

If it were me I will let my husband know how I felt and that I wasn't going to these events anymore if she is there.  It is really up to him to handle it with the ex and with his family.  His mother should care a lot more about her own son than she does about the ex DIL.

The kids will be just fine for what 4 or 5 meals a year without their mother.  She is not alone she had a party of people waiting for her which clearly shows her intention!!  The kids are most likely in on her handy work.  I know my step-kids have been many times.  BM probably makes them beg DH to let her come saying she will be alone.  It is time to cut these ties.  No one including your in-laws want her there so you DH needs to get this taken care of asThanksgiving is only about 6 weeks away.  

Did you see this behavior during the 4 years you were dating??  If so, why did you marry this guy?? Time for some real talk with your DH.  And maybe with yourself if you didnt address this behavior before you got married.