What's this "no food in the bedroom" bullshit?! That's against the Geneva Convention, I'm sure.

That's kind-of a red flag... Clearly your parenting styles are very different

You wouldn’t be the first fiancé or GF or step mom or dad that children have done everything possible to pick a disagreement with because they have the magical idea that if you weren’t in the picture Dad would magically get back together with mom. Young teens are the very worst at this - Younger children are more adaptable and older children are usually more realistic. My teenage son was a huge problem for me and my wife to be. My Dad’s teen daughter was a problem for him and his second wife. I don’t know what to tell you other than what they are saying is likely only part of the issue. The real solution is that their Dad needs to set them straight on what the house rules are when they are at his/your house and who makes those rules. If they are old enough it might also be wise for their Dad to explain that no matter what he’s never going to be with their mom again and that the reason is between their mom and their dad and has nothing to do with you.

try making a point to be their friend first. seriously, every time I saw a step parent try and parent off right away it failed spectacularly. my step father chose to be the friend figure (father stayed in my life growing up). you don't want them feeling like you are trying to replace their mother in THEIR life. If they feel you pushing them or her out, they will push back.

thats too many rules for a “step mom”

Tyrannicaly restricting children from eating and sleeping, how did you expect that to go?