When a property is jointly owned, any one of the owners can "force a sale" to get their share. You may have a lawsuit or claim against the original title company for deeding that property the way they did. Your father was married but they stated he was unmarried. In CA, all property purchased during a marriage is considered community property. The house should have been deeded as joint property to a husband and wife with a tenancy in common with you, a single man. It appears someone was trying to pull a fast one. Or the title company just screwed up. But every time I have purchased and refied property in CA, the title company was very clear about getting it deeded properly. Anyway, just because it was deeded improperly, it does not mean your mother doesn't own a third (or whatever the split arrangement was). The law is clear, in CA, all property purchased during a marriage is community property. There could be a few exceptions, such as
one spouse inherits some money then buys stocks or investment property with it. Since an inheritance is NOT community property, the other spouse would have no claim. But there are ways around even that.