This is a strange question, but I don't know offhand if "ancestors" has a different meaning in religion than in everyday use. Like #3, I don't associate the word "ancestors" with anything other than my parents, grandparents, their parents, etc. It's not something you have to believe it, it's something that is verifiable. I don't see how any religious belief would preclude belief in your parents.
Well, I never saw this before. Something to think about.
Ancestors don't have to have any mythical power. In most religions, the people who die before you go to some kind of afterlife and are waiting for you. Although some people believe they can intervene in your life or send you messages, in most cases it's just comforting to think of them being there.
I think it would fit okay with Catholicism at least. If you understand the ancestors not as gods but rather as saints, then you are okay. Catholicism holds that saints can intercede with God to help the living. If a person thinks of ancestors in this way, it would not be that much of a problem.