I think one thing to realize, you aren't his parent, and you might get a whole lot of rebellion if these are "your" rules. I think this is the case where the father needs to step up and enforce the rules, especially since he is a full time parent. You both should sit down and make the rules so you are both know fully what they are.

I am a step parent, but they are in their late 20's now, and I made some mistakes and one was trying to be their parent. It isn't that they don't have to listen to you, they should, but the rule setting is best left to their parent, especially the discipline.