I have 3 step kids 8-12, and I started out letting their real dad do all the discipline. Then, I'd only discipline them if I was the only adult present. I would say, 'I know I'm not your mother, but I am the only adult here, so it's my job to keep you safe'.

I also will intervene if something they are doing affects my personal belongings. It's been about six years since I've met them, and they are at a point where they know to listen to me. Now, I will occassionally say something even if dad is in the room, but I do try to let it come from him as much as I can. I also try to give them things to do, and negotiate how much time they get on the puter or xbox, or who picks the dvd hire, or things like that. Also, they listen really well with things like chores I give them, especially if there is a reward at the end of it :-$

The two elder boys don't seem to think they have to listen to anyone when it comes to beating each other to a pulp. However, if I sit between the two of them on the lounge (for some reason that's where it always starts) then they instantly stop. And they're bigger than me lol. I think it's because their dad told them I'm very delicate and they could break me

I guess the main thing though, is to get a bond going first before even starting to worry about discipline. Obviously there are times you won't be there, so keep the discipline minimum to those times. Too much too soon is a recipe for resentment on both sides.

Good luck, and just give it lots of time