Do they ignore/go against your opinions because those are your opinions or do they just do whatever they want to do anyway? If it’s the former, you can express the opposite of your opinion, which might having them lean a little more towards what you want. Otherwise, my general policy is to not interfere in others’ matters anyway. At most I’ll mention my opinion casually when I think it’s important, after which I consider my responsibility in the matter fulfilled.
As for the children, I don’t think they’ll really be affected by this much unless you let them be. As long as they’ll feel loved by their parents, I don’t see this as something to really worry about. What that means for you is to stop expecting what you’re not going to get and don’t let it bother you when you don’t get it.