Witchipedia

Um. Witches are human.
Contacting your ancestors is sort of a gray area between magick and religion and the answers are usually going to be based on some sort of faith. I honor my ancestors, and when I contact them it's usually to give thanks and sometimes to ask for advice, but not favors. The thing about ancestors (according to my religious belief) is that they generally want to help out their descendants anyway. Evolution, after all. Most of my ancestors were Christian, but I"m not sure the dead are religious. After all, religion is all about faith and belief in the unknown, but the dead have already gone and have it sorted.

As for asking any spirits for help with spells. The whole point of a spell is to overcome the material part of ourselves that interfere with the direct connection to the energy of the Universe. Spirits, including the dead, are made of energy. They don't need witchcraft.