Legal Question in Real Estate Law in California

No you don't have to give him anything. His tenant might have a contractual obligation to inform Landlord if he has sub tenant but you are not paying rent and your cousin has the right to have visitors at the very least. Who told the Landlord that you actually lived there when it's just short term? Landlord really can't do anything to you but might try to evict the tenant Eithet way, he can't just evict the tenant and say that means you have to leave too. He actually would have to evict both of you now if it came to that and that's why he wants your name. This is just typical landlord bullying. You should get an attorney to write him a short letter. I would charge you a reasonable price to write a simple letter. It would take me no more than an hour.

I'm not so inclined to call this typical landlord bullying. I don't represent, nor do I favor, either landlords or tenants. The landlord seems to be following a course of action that's suggested in very popular paperback self-help law books with titles like "How to be a Landlord" or "Landlord-Tenant Law". There is a tendency for residential leases in California, perhaps fostered by books of this kind, to suggest that landlords put restrictions on guests in their leases, so they don't unintentionally acquire subtenants. One such book suggests that leases require landlord permission for guests who stay more than ten days in any six-month period.

So, therefore, your cousin first needs to find his copy of his lease and review it very carefully to see whether it contains any references to guests. Even though you (probably) aren't a sub-tenant or a co-tenant, check the lease to see how they are defined and treated.

The next issue is how the heck the landlord knows about your presence after only a month, and what the heck triggered his indignation. Most guests in rentals aren't quickly nor easily identified by most landlords. Is the rental in the landlord's granny unit? Did a moving van full of furniture show up?

It's very hard to give advice as to how to handle this problem without full knowledge of the setting, the lease terms, the landlord's reasons, and much more. I think the starting point must be to see what the lease says about guests, occupancy and use. Whether your moving in was quiet and low-level or created a ruckus is another issue. While I wouldn't necessarily concede to the landlord's point of view that you must disclose all your personal identification and information to him, neither would I automatically assume that a one-month guest must submit to landlord scrutiny and become a subtenant or co-tenant.