They can be vanquished with a simple Power of Three spell.
After a few centuries, the Anubii became weaker and they visited a witch to ask for a spell that would make them demigods again, but when the witch couldn't help them, they killed her and drank her blood. After that, they found out that the blood from a witch made them stronger and they could live forever. They started collecting the blood of witches and Wiccans throughout America, until they were vanquished by the Charmed Ones.
The Anubii have appeared in a total of 1 non-canonical novel throughout the franchise.