Legal Question in Real Estate Law in California

No. You will need to give them a 30-day notice then initiate an eviction action against them if they don't leave voluntarily.

I am inclined to disagree with Mr. Hoffman. Assuming the buddy was renting the trailer on a month-to-month basis, he would become a trespasser on the 30th day after the buddy made his last rental payment (or when it was due, anyway) under the Court of Appeal's decision in Miller & Desatnik Management Co. v. Bullock (1990) 221 Cal.App.3d Supp. at page 13. The court said, at pages 18 and 19:

"We therefore hold that under section 1934, a month-to-month tenancy is terminated by notice of the tenant's death; further, the tenancy is terminated as of the 30th day following the tenant's last payment of rent before the tenant's death. No further notice, for example under section 1946, is required. This preserves the tenant's or her assignee's right to possess the premises for the remainder of the month, the period for which the tenant has paid rent, and prevents the inequitable result of requiring the landlord to participate in a potentially indefinite lease with a tenant he never contracted with in the first place."

If the buddy had a lease from you for a definite term, the lease would remain in effect and the wife and daughter would, if they are the buddy's heirs, inherit the remaining lease term and therefore would not be subject to eviction following a 30-day notice. See the cases of Joost v. Castel (1939) 33 Cal.App.2d 138, and City of Los Angeles v. Greines (1930) 107 Cal.App. 481.

If the buddy had neither a month-to-month rental nor a lease for a definite term (like one year), but was instead your guest, the ex-wife and daughter would be trespassers from the get-go and should leave upon your ordering them to do so.

In none of these three situations is a 30-day notice followed by an eviction action the appropriate process, in my humble opinion.