Legal Question in Landlord & Tenant Law in California

It would be extremely unusual and unlikely for a family to own an apartment building and "just find out" that they own it after paying rent to a purported landlord for some time. If that really is legally and factually correct, there is almost certainly some kind of legal mess involved that will not be sorted out without the help of a lawyer. They really need to make an appointment for an initial consultation with a local attorney.