Good points littlebluechair.
The question popped into my head the other day - would it be better if DSCs just lived with their mum and never saw their dad, thereby avoiding all the conflict and uncertainty over when they'll see their dad (as the Ex constantly changes dates - long story for another day)?
A little bit of me thought, maybe... and then a much larger part of me thought, no way! DP is their dad, and a very good one at that (Ok, I know I'm biased!). He's been a huge part of their upbringing and its obvious to see how much he means to them and how much they benefit from seeing him. It's our responsibility as their dad and step mum to minimise the harm that the conflict brings. We can't control what ExP says and at the moment we can't stop her changing weekends (I've got a feeling it's going to end in court...) on a whim, but what we can control is how we act. We did try involving eldest DSS in discussions once (he's 9) but it obviously distressed him as he didn't want to have to make choices between seeing his dad and doing other things. So we learnt from that - at the moment, however tempting it is to get him 'on side', it's not fair to do that to him. So we can make sure that, however bad we're feeling about everything, we don't speak badly of the ExP, we don't question her authority in front of the children, we try to explain everything clearly and fairly to them, we take responsibility for what's happening (so they don't feel they have to), we don't argue with ExP when we see her and we're positive and loving when the children come to stay. As littlebluechair says, we're providing a positive example to the children.
It's not easy, and I admit that sometimes I cave (normally by crying with frustration rather than saying anything bad, but still don't like doing it in front of DSCs), but then I'm sure there are other parenting situations that are equally difficult, where you have to stay strong and put on a brave face for the sake of the children. The main thing, I think, and the hardest thing, is to keep your role as a parent/step parent, and your role as an ExP/partner of someone with an ExP separate - so the rage and negativity has to be dealt with in the latter role, so it doesn't spill into the former. Much easier said than done sometimes, but I'm learning a lot about people and relationships!