Big blended family Our kids don’t get along how can we stay together

I’m a (32f) been in a relationship with a (33m) for a year but we’ve been friends over 20y I have all boys 15,11,3,2 who live with me and he has all girls who live at home with him 10,9,8. We had a stillborn child this year so are really attached to each other but the situation also caused distance mentally for me. We also have different parenting styles he’s more strict his kids have more rules but have more behavioral issues and I’m the laid back/fun mom he calls me my kids pretty much do what they want but aren’t bad kids they just can be a little loud and mouthy at times but not disrespectful my partner sees it as otherwise and is having a harder time connecting with the boys. We’ve been talking about becoming more serious the word marriage has been tossed around quite often. My boys really don’t care as long as I’m happy even though it’s not a stepdad they would have picked but his girls are obviously not happy it seems they are jealous of my children because I’m affectionate and give them nice things even though I don’t treat them any different they want all my attention to point where they will lie on my boys to get them in trouble major lies not small ones and or try to break me and their dad up cause they want all of his attention atp so many lies have been told that it’s been best to just keep the kids separate. Which means his kids are gone more often almost never around he spends more of his time at my house with me and my kids I don’t feel like that’s fair to his kids. our overall relationship outside of the kids has been pretty good but how can we make it work if we can’t be together as a family I don’t want to walk on eggshells around our kids or would it be easier to leave I don’t want my kids to feel like I’m picking anyone over them or him vice versa with his kids