Legal Question in Real Estate Law in California

Anytime I read any thing about a real property deal with a verbal side agreement, I immediately turn and walk away.

If the facts show that the four owners are in a partnership, and they may well be, whether they think of it as such or not, then the oral agreement regarding continuing co-ownership (or whatever) very will might be an enforceable oral partnership agreement (or part of one). Not all co-ownership of real property results in a partnership, of course, but when four adults are on title to one parcel of real estate, there's often a strong possibility that they are conducting a rental or investment partnership, whether they've used the term to describe their business relationship or not. Consequently, the situation may not be governed by the general rule that agreements respecting ownership of real property must be in writing. My advice would be to try to negotiate some kind of an exit arrangement acceptable to all, and reduce it to writing. Avoid litigating this issue, if possible. It's not possible to predict a winner (from the given facts) if this were to go to litigation.