Legal Question in Real Estate Law in California

"Rent free" would suggest that he's not a tenant or a lodger, two categories with significant legal rights. Therefore, he's probably legally a "guest" -- and a guest becomes a trespasser when asked to leave, given a reasonable amount of time to do so, and then they don't. Ask your local sheriff or police how they deal with removal of trespassers. Each jurisdiction has its own priorities and problems with enforcing the law, and they will vary in whether and how they will assist in removing trespassing family members.