Step siblings

I would be grateful for any advice on step siblings.

They’re not really step siblings at the moment but my bf and I have been together a year and a half and we’ve discussed moving in together and getting married as soon as his house is sold. He does come over and stay a few days a week (we live a little over an hour from each other and work opposite schedules). He gets his daughter every other weekend and usually they come over and stay at my house.

For a little background: I have 8 year old twin boys and I’ve pretty much had them by myself since they were 5 months and they see their dad about 5 weeks a year since he’s numerous states away. He has a 7 year old daughter. She’s really sweet but used to being an only child and only grandchild on her dads side. She can be bossy and tattles a lot. She’s also very deprived for attention as her mom and step dad don’t pay her much attention. That’s another story and we’d likely try to get custody once he fully moves in and such. My kids are used to being around each other and go to a childcare during the day where they are constantly active and are more reclusive when they’re home on the weekend. They just want to relax and then play here and there. One of mine is also really bossy and clashes a lot with his daughter. I think she just loves him and wants to play with him nonstop and he just wants her to leave him alone. It’s a constant battle. Mine aren’t used to being around a sensitive girl and she’s not used to sibling squabbles or being around kids outside of school really. Even BF admits she was never really socialized since her mom stayed home and never got her around other kids besides 2 of her cousins until she went to school. The son she really clashes with finds it hard for her to play with their toys. He doesn’t like sharing too much even though he’s had to his whole life but I guess it’s easier with his brother by more difficult with someone new. Sorry I’ve gone off a lot of different directions here.

So back to the point. Anyone have any advice to help them get along? I think that once his house sells and then we get a 4 bedroom house so she has her own space will make things better to a certain degree but we may be a long way from that.