Legal Question in Wills and Trusts in California

You deal with threats the same as in any context. If it rises to the level of criminal conduct you report it to the police. If it is civil harassment, you file for a restraining order. If neither of those apply you put up with it. As for preventing you from settling the estate, that is way to vague even to begin to answer. It would depend entirely on what they are doing and how it "prevents" you from settling the estate.