My landlord has complained that when my 22yr.. old son returns from college in the summer to stay with us, this is a violation of our rental agreement because it constitutes a long-term stay or extended visitation by a family member. What length of time is acceptable by California law for our son to be able to stay with us?

In my renters if it was over a week, we considered it extended.
Did not list your son as a resident, that would be living there part time.