I don't include SS12 in very much. My two are two years apart and much younger. Why should I bend over backwards for a kid who's not mine? And one who is being raised with different values and is in his way to being alienated? SMS have to give up so much already, why do we not get special things just for our own kids? And we have taken photos without him. And I've had just my two on Christmas cards. He is long distance and we don't see him much. Before Covid, SS would come here 2-3x a year and DH would go see him on his own. Don't feel bad about doing special things just for your two. Skid is not your responsibility.

I don't have kids, but it seems to me that you should be able to do both - pictures with SD and pictures without.

I'd do the growth ruler anyway, who cares if SD's starts at 8.

In other words, it's a balance - and your DH doesn't get the final say.  It should be a negotiation and a compromise. You will have to compromise on some things, him on others.

My nearest sibling is 8 years younger, my sister was 10 years younger and the youngest is 17 years younger.  I wouldnt worry too much.  That age gap is huge, insurmountable.  You will probably end up being glad to have her, I did a lot of babysitting!  My mom was custodial but you only have SD 4 x a month but still, she can keep an eye on them while you do something else.  She is in a different life stage from your girls.  I think it will be okay

We don't get SD12 nearly as much as you get yours. When they become preteens they don't want to visit as much.

Anyway, create your traditions and go forward with them whether SD is there or not. If she's there on Christmas Eve she can put out cookies and hang up a stocking, if she's there on Christmas day she can just find her stocking, do you know what I mean? Traditions and events shouldnt have to be planned around her schedule, and as she gets older you can be sure it will get less and less regular. Make traditions more about events and times and that way she will be there for some, not for others and learn that's just how it is sometimes. 

As for the things specific to your girls, you reserve the right as a mom to get to do those things. You don't have to make up for something BM and your DH didn't do with SD. She had plenty of other things and experiences. 

For some of these things, like matching outfits and growth charts and Santa plates, I'd do what it is YOU want to do. Your SO has had the same ability to do those things for SD, and if he now finds it important, then he can put in the work to do it for himself. It's not on you to develop traditions for his kid if he isn't developing them first.

There are things, though, that I think you'll have to compromise and include SD (though this is still somewhat dependent on how your family operates). If, for example, you and SO can only do one vacation a year, or if it's a kid-friendly vacation to somewhere like Disney World, it would be cruel to not include SD, both to her and SO. BUT, it still becomes your SO's responsibility to figure out how to pay for/accommodate SD. That may mean SD bringing a friend, or having to rent a condo or conjoining rooms, or finding clubs/programs for older kids, etc. 

Now, what I DO think you need to do is find a way to get out of your own head and stop letting the mere thoughts of SD ruin these activities. Likely, it's not her that ruins them; it's how your SO treats her and the situation that does. He SHOULD be incorporating her into family norms and teaching her how to act like part of HIS family, too. Kids can learn to act differently at different places.

I am an Irish twin (almost exactly 9 months apart) and I’d have to say you’re going about this wrong on two levels.  My mom was very careful to treat my sister and I as individuals.  Yes she would often have an outfit that was the same, but always in different colours . She made sure to allow us to be best friends, while emphasizing that we are separate people.  To the point where she started me in school early so that we would be in separate grades and have separate friends.  It allowed us to have pride in our individuality.  There is nothing more frustrating to an older sister than having EVERYthing shared with a younger sister.  No accomplishment, and nothing goes by without be compared or shared.  While your SD gets everything to herself.  On the other hand, you seem to be so focused on recreating your sisterhood bond that you’re willing to shove an innocent 8 year old aside because she doesn’t fit the picture you have in your head of “your girls”.  I’m sure your DH would love if all three sisters eventually formed a tight bond that lasted them long after you two are gone.  But she won’t if you don’t encourage it.

So for pictures – compromise.  Do some of each grouping.  For the Santa plate – I have one with no names.  If you have the names of just your girls, you push SD aside as “not worthy” or “less”.  And besides that, when your girls grow up you have a plate with their names on it.  Without the name you could pass it to either of them to use for their children later in life.  Or keep it to use at your house when you’re a grandparent.  Same for the growth chart.  If you do one for each of them individually, you still have your mommy keepsake or they can each have their very own growth chart.  And if SD wants one too, where’s the harm.  Rather than something in the living room that actively leaves her out, you could have one on the wall beside each bed that gets used equally (measure each of them on their birthday, or on special occasions so you don’t simply buy one, but still refuse to honour her feelings by not using it).  You think of her as grown up at 8.  Wait until your girls are 8.  You’ll realize how small they still are.  As for vacations, SD goes on the big ones, you plan smaller ones when she’s with her mom.  I’m sure your DH would love to make wonderful memories with all of his daughters.

So for me – focus on your girls being individuals, not a collective “your girls” vs SD the intruder.  I have three blended girls.  They didn’t start that way, but now as adults the kids are tight.  Because we taught them the value of siblings.  All of them. It ebbs and flows, but they have each other because we treated all of our kids equally wherever possible.

We have skids 50/50. We don't wait for them to be here to do things,  nor do we exclude them if they're here.  We don't do professional photos, so that's not an issue.  If I wanted a cookie tray with just DD's name and thought DH would be upset if I excluded the skids, I'd have my mom gift it to me.  DH can't complain about that. 

Skids recognize that there's an age difference (4.5 and 7 years between DD and SD5 and SD8, respectively), so for some things I do just for DD I'll tell them it's for babies and they're too old for it, and point out things they have or do that DD doesn't. They're fine with it, as is DH.

I feel no guilt at all when I do something for or with my DD that I don't do with them.  I treat them well and include them in a lot,  plus they have an involved mother who does a lot for them. 

I think that the age difference will somewhat take care of some of these issues.  like the trips...some trips are not going to be attractive to an older child or teen if they are planned with toddlers in mind. and as she gets older inviting a friend can be a good way to keep her occupied and reduce problems.  We found it worked well with my sd's if they had a friend with them.

the santa cookie plate ... idk.  why does the special plate necessarily have to have "names' on it at all?  it could still be a special commemorative plate without names... and if it will be a keepsake.. "which" of your girls gets it later in life.. ??? I might either go with "no names" or get three little plates made with each girl's names... it won't hurt your kids if she has a plate too. and it is a nice gesture...if you do a special plate for each child.. each of them gets to keep it for "life".

i think it's perfectly fine to get some portraiture done of just your kids.. I mean, your side of the family likely would not have interest in having SD in every picture.. and there is always a chance you could split with her father.. that would make having all pictures include the three awkward.  You could also include her in the photo shoot but ensure that there are pics of solo and different groupings... leaning more towards the shots you want.. but would still have some "sisterhood" pics with their half sister.

There's a large age gap anyway so hopefully in. Few years it'd be considered not cool by the step child to have a santa plate etc etc. Do you specifically have her Christmas eve or day anyway? Put the grow chart in one of your children's rooms so it's not in step child's face?

I don't deliberately exclude ss here but equally so much has gone on I guess I've trained myself not to let him or his enter my head until he's here. So, when buying cutesy stuff for bd I just buy for her. One year my dd came running down proudly showing the grandparents her personalised santa sack. Ss looked a bit put out and said don't I have one? 'Oh sorry, I didn't think as you're never here for Xmas day, perhaps your mother can get you one?' 

I take it there's a bm in the picture who it could be up to to have already created such traditions for the child? 

My ss isn't the one who complains, dh is. In front of ss.

My standard answer is... that I, as a mother, choose to take my children and my spouse on a trip / buy my children things / have traditions... and that ss's mother is completely able to do those things with HER kid, as a mother, with her own spouse (short term boyfriend but whatever), and that I have no more obligations to include her kid in things to do with my kids, than she does to include my kids when doing things for/with hers.

His argument is always that it's not fair to ss... and my response is always that it's not my problem if his mom can't give him what I'm able to give mine.

It generally shuts him up.

Do whatever feels right to you. SD also has a mother to do cutesy mother/daughter things with. And I doubt SD's mother will think oh, poor little half sisters will miss out. And yeah, some kids are just more delayed than others. I have no problem with leaving DD with my friend's 7 and 12 year old to play outside on the street. Whereas her cousins who are slightly older would probably watch on as she got collected by a speeding car.