Legal Question in Real Estate Law in California

Well, yes, there is a way - a special kind of lawsuit called a partition action, and designed to allow an unhappy co-owner to petition a court for an order dividing the property. It used to be done by a lot split, but with urbanization and zoning laws, the more usual practice is for the court to order the property sold and the net proceeds divided in proportion to their ownership interests after adjustment for more-than-fair-share contributions by one owner for necessary expenses such as mortgage payments, property taxes and insurance.

It's not exactly clear what happens when a partitioned property is upside-down and the sale produces less than enough to pay off the mortgage. One well-known treatise suggests that the antideficiency laws would apply in the same way and to the same extent as in a court-ordered foreclosure sale, i.e., as though the partition were a judicial foreclosure. If so, whether the two of you would be liable for the deficiency could depend upon whether the existing loan was a purchase-money loan or whether your parents had refinanced.

Anyway, many unexpected things can happen once a partition suit is filed and served. The other owner may start paying his share, or he may propose to buy you out, or offer to be bought out on good terms, or may suggest a private (out of court) sale of the property. Maybe you would be the high bidder at the partition sale. (The method of sale in a partition can be through a broker like a normal property sale, or an auction, and the owners can usually choose the method and the broker if they are willing and able to cooperate; otherwise the judge will call the shots).

However, as you can see, one very likely result of a partition suit is that BOTH of you will end up "off title."

Why would he want to remain on title? Probably is hoping your investment in mortgage payments, insurance and taxes, etc. will keep him invested at your expense until property values go back up.. You are both technically liable equally for the expenses, even though your live there and he doesn't, because you both technically have the right of possession and neither of you is obligated to pay rent to the other. As a practical matter, it is common for co-owners to have either a formal, informal, or merely understood agreement that X will temporarily give up his right of co-possession if Y will handle temporarily certain expenses.