In front of the kids? I would never contradict him so if, for example, he's said bedtime at 8, I would not reply no, kids, go at 9. (ignore your dad) In those cases, if I felt strongly, I'd get him by himself and say my bit and we'd agree and if we agreed that he was in the wrong
then HE would go to the kids and say actually, chaps, I have changed my mind... I wouldn't say I've said dad can't...
but if we were having a conversation about something either in front of the kids or including the kids, and he said (for example) what do you think about bedtime at 8, I'd certainly say yes, sounds ok, or we could watch a film first and that would mean bedtime at 9/I think 8 is a bit early, how would you feel about 9
because while I don't think it is acceptable for the children to see one parent saying (basically) no, I don't care what you just said, we are doing this instead, I think it is good for the children to see parents discussing something, exchanging views, listening to each other's views and reaching agreement.
I know that's really badly put together, but I hope you can wade through it and get what I mean 