Haha, yeah.....

Peeing in strange places like this can be a sign of stress.

I agree though, if you invite the dogs up onto the bed but, at the same time, assume they know they shouldn't be up there. Just because they might give you that look doesn't mean they know they shouldn't be up there.
Things like this can be very confusing for dogs which is why it is always best to stick to one thing. Either they are allowed on or they aren't, full stop. You can't really expect them to understand a half way agreement.