Legal Question in Civil Litigation in California

You have offered no reason to believe your assialant's grandmother is liable for his actions. Even if you can prove that she knew he was violent, that's not nearly enough. Lots of people may have known the same thing. That does not mean they are responsible for the harm he causes. She might be liable in some very unusual circumstances, but nothing you have said suggests that such circumstances are present. The fact that the grandmother owns property has nothing to do with whether she is liable.

Bear in mind that baselessly suing someone is abuse of process. If you sue the grandmother without valid grounds and she wins, then she may be able to win a lawsuit against you. She'll have to prove both that you lost and that there was no reasonable basis for your claim, so you should make sure you have a plausible case against her before you name her as a defendant.

Good luck.