Legal Question in Real Estate Law in California

They definitely could. Making the tax payments on property is one of the elements of establishing what is called "prescriptive title." There are numerous other factors and nuances to obtaining prescriptive title, however, that would turn on all the facts and circumstances of the situation. You definitely should hire an attorney to give you a formal legal opinion and advice on dealing with this.

Yes! Mr. McCormick has confused "prescriptive title" with "prescriptive easement," but conceptually he is right. The legal concept is "adverse possession." Acquiring property by adverse possession requires continuous and open, notorious and hostile possession, plus payment of all property taxes and assessments, for five or more years.

Continuous possession doesn't mean you can never leave to go to the grocery store. What it means is that the record owner doesn't come back into possession during that time. Also, the possession needs to be open, notorious and hostile, but this is just legalese to say that if the possession of the claiming party were permissive (for example, if he had a lease or license or some kind of permission to be there), it would not qualify as adverse.

Maintenance of the property is not a major issue. Payment of the property taxes is major. That, along with possession without permission for five consecutive years may cause the owners "of record" to have lost their ownership rights. If so, your family are now former owners, and the adverse possessor can get legal (record) title by bringing a quiet title suit, to which your family may have no defense.