I'd say even one's parents are technically ancestors, though they might not take kindly to being referred to as such :)
I think all ancestors are relatives, but not all relatives are ancestors. Aunts and cousins and such are relatives, but not ancestors, as you are not directly descended from them.
I wouldn't go that far. I think your great grandparents are relatives, and anyone further back is an ancestor. I might stretch to great great grandparents, but I don't think I'd go any further