I’m the poster who shared my experience with the two step families. While they were on opposite, extreme ends, they were both abusive to me. By sharing, I was wanting to show how not meeting the children’s needs in blending families can be harmful to the children.
OP has presumably been with her husband since DD was a toddler. It would be a reasonable expectation for DD to consider him a father and to consider herself part of his family. Based on her posts, OP seems surprised and upset that his family doesn’t consider DD one of them and she seems concerned that this will hurt DD.
I shared because being excluded hurt me. Before marrying SF1, my mom should have made it clear to him that she expected me to be considered part of the family. He didn’t have any children, but he should have communicated to his family that he expected me to be considered his daughter and treated as such. When they refused, my mom should have refused to have me around them and refused to have them in our home. She should have given SF1 the ultimatum that he step up and behave like a father by loving and protecting me or the marriage is over.
On the flip side, DSD doesn’t want to consider OP as a mother figure and DD as a sister. I suspect, based on her age, that this is probably partly in response to the attitudes of the adults around her. No matter the reason, her boundaries in this should be respected. I suspect there is more to her refusal to stay overnight. I wonder if she went from having her own room to sharing with her new sister or something similar.
My second step family expected me to immediately become one of them the moment my mom married SF2. It wasn’t just that they wanted me to reject my paternal and maternal families in favor of them. They had a weird patriarchal thing where SF2’s dad was head of the family. Everyone’s values, religion, hobbies, likes and dislikes, down to food preferences , were supposed to mirror his. I was also expected to feel instantly bonded with people I had met two days prior the moment my mom said her vows. SF2 had children who I was supposed to consider siblings and because I was several years older, I was supposed to take on the role of protective older sister. My mom should have insisted they respect my boundaries and allow me to be myself or not allow them to stay in our home. Because she didn’t advocate for me when I was a teen, as an adult, I don’t have a relationship with them and have a limited one with my mom.
OP and her husband need to work out what is best for their respective children. If DD needs OP’s husband to take on a fatherly role, then OP needs to insist on this or end the relationship. Husband can explain to DSD that DD is now family and while it doesn’t in anyway diminish his love for her, he also loves DD. DSD has already made it clear that she doesn’t want a sisterly relationship with DD, so OP needs to help DD respect that boundary. OP needs to put the wellbeing of her DD first. If DD is going to be hurt by SF’s family excluding her, then OP needs to seriously consider the future of her marriage. If OP’s husband doesn’t love DD enough to insist she is treated as family, I wouldn’t recommend OP stay married to him. OP, her husband, DD and DSD need to be in a combination of family therapy, individual and marriage therapy. The response to this wedding is a symptom of some massive underlying problems.