Older kids

Me and my bf have been together a little over a year and a half. Coming into the relationship he has a 10 year old girl and I have a 9 year old boy. Our little boy together is Almost 2 months old and we constantly fight over the older two kids because he has a different set of rules for his child then I have for mine. Despite all of my efforts to get him on the same page as me all have failed. I have rules for my child ( don’t stay up all night playing video games or you have to eat all your dinner to get dessert (I also don’t make separate meals for everyone I was raised to eat what was cooked) every time I try to make rules for the kids mine follows them and his doesn’t (nor does he reenforce them) am I being too crazy to think they should have to follow them same rules