Tenants refuse to vacate premises

[George Alves Jr]

The tenants have lived rent free in this home for many many years.  The owner is elderly and former father in law of the tenant.  Her son (owners grandson) and his girlfriend also live in the home.  The owner does not want his tenants out on the street.  They are on a low and fixed income and likely battling addiction.  Would anyone have any ideas on how we can get them out of the house and keep them off the streets?  The home is in San Diego County.  Any feedback would be greatly appreciated. Thank you.