If the suite is not legal and the person living there has no lease agreement, then it is possible they may be classified as a lodger instead of a tenant. In the case of a single lodger in a house where there are no other lodgers, the owner can evict the lodger without using formal eviction proceedings. The owner can give the lodger written notice that the lodger cannot continue to use the room. The amount of notice must be the same as the number of days between rent payments (for example 30 days).
Iâ€™ve attached a link for the California Tenants handbook. See pages 4 and 50. If you have any questions concerning the legality of your actions, please consult a real estate attorney. A 30 minute consultation would be enough to provide you with all the information you need to make an informed decision.