Co-tenant vs occupant vs subletter: know the difference
A co-tenant usually signs the lease with the landlord and shares the tenant obligations under that lease. An occupant lives in the home but may not be a party to the lease. A subtenant generally rents from a tenant—often called a master tenant—rather than directly from the owner.
Those labels are not interchangeable. They affect who collects rent, whose permission may be needed for a replacement, and what rights or obligations apply if someone moves out. In San Francisco, a master tenant can be treated as a landlord in relation to a subtenant.
Before paying a deposit, ask for the lease, identify everyone on it, and put your own agreement in writing. For an actual dispute, get advice from the San Francisco Rent Board or a tenant lawyer.
Sources: SF Rent Board guidance, California Civil Code.