Just trying to clarify. Your Dad and his wife are living in the house that your father is on the deed but his wife's name is on the mortgage? Is that correct? If his wife is on the deed also then she definitely is part owner. Without knowing all the details about the deed and how they are holding the property, it is going to be tough to answer your question.
CA is a common law state, so it makes things more complicated. Even if you dad is the only one on the deed and his wife is on the mortgage, because they are married it could mean that they would each be entitled to half the property.
Without knowing all the details of the situation, I would recommend contacting a real estate attorney to look into the details of the current situation and what options there are.
Hope this helps!
Alain Pinel Realtors