No, the only way to remove one of the Lords of Hell from a host body is to kill the body. Once they take root, they completely override the will and mind of the host. Even one of the Horradrim's most powerful mages - Tal Rasha - was unable to keep Diablo's brother Baal at bay on his own.

The Nephelem were the first humans; the sons and daughters of angels and demons. Over time, humanity became less powerful for some reason. Uncle Deckard said it was something to do with the Worldstone suppressing Nephelem power, but... nobody knows for sure.