2 kids want adoption, 1 does not

DH and I were each married before and have children from our first marriage. Our families were friends when our first spouses were alive, and in fact my first husband and I spent a lot of time taking care of DH's daughter after her mother died (she was 4, is 11 now). She bonded pretty closely to me over the years and is thrilled that DH and I are now married. There's been some bumpy adjustment periods but generally she's more than ready for me to be mom. My kids are a different story. My daughter was six when her father died, and is the only one of the kids with a clear memory of her deceased parent. (My son was 3). She is very resistant to DH, pushes him away emotionally and will sometimes refuse to speak to him even if it means waiting hours until I come home from somewhere to deal with whatever the issue is. She has made it very clear that she does not want to be adopted. I think my son would like to accept DH, but he is holding back because he's following his sister's lead. My daughter is also very resenting of the relationship between me and DH's daughter. They are very close in age, 10 and 11. What do we do? DH and I want to stepparent adopt all of the kids, but my daughter clearly expresses that she doesn't want it. She is not old enough that she has to consent to an adoption, but I worry about doing it anyway when she says no. I think adoption would be best for my son - when I ask him by himself, sometimes he says yes, sometimes he doesn't know. And DH's daughter clearly wants me to adopt her and gets mad at me that I haven't made it happen yet. Should we wait on adoption to see if she comes around? I don't like to make the other two wait, especially my stepdaughter since she really wants it, but I don't like the idea of forcing my daughter into it either. Should we adopt my stepdaughter and my son, but respect my daughter's wishes and not adopt her? I don't want her to get worse and feel like she's not part of the family because she's the only one who didn't get adopted. I'm so confused about what the best course is. Please help!