It sounds like your landlord may have violated the warranty of habitability, which provides in pertinent part, "The lessor of a building intended for the occupation of human beings must, in the absence of an agreement to the contrary, put it into a condition fit for such occupation, and repair all subsequent dilapidations thereof, which render it untenantable."
In California, you have a right to demand that all repair work where the value of the labor and materials exceeds $500 be performed by a licensed contractor. Without knowing more about your particular fact situation, I cannot opine as to whether or not the damage/repair job should have cost $500. Do you know whether the son is a licensed contractor? You might also want to bring in an outside hazardous spill remediation company to get an estimate of what a proper cleanup and repair would cost.
What was the basis of the 90-day notice? Typically 90-day notices are used in Section 8 or other government-supported housing, or after a trustee sale (foreclosure).
How long do you have left on the 90-day notice? You may have time to send a demand letter highlighting those things that you want done, including remediation and repairs by a licensed contractor.
Have you been injured by the leak, or by any other dilapidations? You haven't specified what the nature of the illness was, but you may also have a claim for personal injuries.
How long did you have to stay in the hotel? There is a non-profit, Fair Housing Napa Valley that can provide more information, and Legal Aid Napa Valley also represents tenants. The Napa County Bar Association also has a link on their website to landlord/tenant practitioners.