How to handle a subtenant subletting process

[Natsumi Jang]

I have a single family home in California. It seems I have 3 master tenants on the original lease. One of the master tenant has moved out. And the remaining two master tenants wants to continue with the original lease. One of the two master tenant found another person to alleviate them with the rent so they can continue to split it three ways. As the landlord can I continue to keep the current lease as is with now only two master tenants? Or am I obligated to add the new person as a master tenant to the original lease? Ideally I just want the new person as a subtenant have that person work things out between the master tenants in a form of subletting. I don't wish to add anyone else to the original lease. Is that possible? Thank you!