Should I feel guilty...NO i dont think so!
For years my husband has been attacking me with this problem. He has a step daughter with his ex wife that he deeply loves and they also have a daughter together. My husband is 32 and I am 22. His daughter is 9 and step daughter 12. #1 I must say i have no interest in his step child. The girl has a smart a$$ mouth and i dont feel like i need to deal with her if shes not apart of him. Im already accepting the BULLSHIT i have to deal with his daughter and ex wife why add more to the equation. His parents and family still accept the girl and bring her around to functions, i dont mind BUT shes not coming home with me! Its really embarassing going out in public especially around my friends when this girl calls him dad and I have everyone asking me questions. And at events his family from mexico practically claim BOTH girls as my daughters. My husband actually said when we have our child his step daughter will refer to our child as her brother or sister. I DONT WANT TO HAVE ANY ATTACHMENT TO THIS CHILD WHATSOEVER. I told him I dont mind him visiting her taking her out to eat and bonding with her. But her mom ruined the chance of having a family for them when she cheated so its not my fault. I think its unfair for him to try and force this on me and make me feel guilty. I feel like he is pushing me away because im forcing myself to "like" his daughter and now he's trying to force the step child on me! I started feeling like this after the EX told him that the oldest didnt like me, but yet she complains about how sorry her mom is when shes around me and smiles and acts all friendly. I can tell hubby is sad because his relationship with his step daughter is declining and sometimes i just feel like calling it quits because of these damn BRATS!
Besides this i must say I have disliked his father very much. I dont know what to do! He picks up my husbands daughter and step daughter all the time for the ex wife without calling my husband first. We show up to events to find the girls there and we look so dumb. Sometimes my father in law will tell the girl now to call her dad because he doesnt want him to know. He has no respect for my husband at all. I think if u want to pick up YOUR sons daughter you need to ask him. Whats the point in him paying child support if his dad has her 3 days a week and her mom only 1 and us the weekend? Its not far for him to take on that role and shes getting paid for nothing! I dont know how to correct this because it has been going on for so long, but i think next time i see them at a function and we didnt know he picked her up im going to say something.
How does your DH feel about
How does your DH feel about his dad's picking the girls up? I think that so often in situations like these, the grandparents think, "just because our son/daughter divorced this person doesn't mean I should have to see my grandkids less."
If your husband seems to be ok with it, or doesn't want to fight it, there's not much you can do about it. I certainly don't recommend mentioning it to FIL at all as that will only make you look controlling. This is a discussion that would go over with FIL much better if DH had the discussion with him.
As for the SDs, you said they're 9 and 12 and you're 22. When SMs and stepkids are relatively close in age like that, problems can arise. SD12 has known DH as Dad for most of, if not all, her life. Maybe you could all benefit from family and individual counseling, including SD12.