Roommates brother moved in and is refusing to leave

Location: California

I moved into a 2 bedroom apartment with a friend, and we signed a year long lease. She decided to move out last month. Her brother came to help her move out.

After she left, she asked if it was ok for her brother stayed behind for 1 week to sell some of her stuff. I said yes. But he’s now been living in the apartment for the past few weeks, and he just told me he’s intending to stay until January.

I told both him and her that I wasn’t comfortable with him living with me. They’re refusing to move him out now.

What options do I have? I don’t want him here, and his name isn’t on the lease.

Author: highwayptrl