Legal Question in Landlord & Tenant Law in California

They are right, not 100%, but mostly. When you rent an apartment as roommates you don't convert the landlord from an apartment owner to a rooming house owner. As between the landlord and the tenants, the tenants are a single unit, like a partnership, renting a single apartment unit, not parts of it. They are all jointly and separately responsible for 100% of the rent. Their arrangement among themselves is irrelevant to the landlord, both legally and in fact. As long as any of the roommates is in the unit, each of the roommates is liable for the entire rent, regardless of whether they have moved out or not. This is why the management company refused the walk-through and keys. All the roommates still have the right to posession and occupancy of the unit, and the management company is correct not to interfere with that by taking the keys or other action consistent with a move-out. Further bad news is that even if everyone had moved out in response to the three-day notice, not only would there be no right to a refund of the partial month's rent, because of the lease the tenants would still be on the hook for rent going forward until the unit was re-rented. Complying with a three-day notice doesn't cut off the rent, it just triggers the duty of the landlord to take all commercially reasonable steps to re-rent the property. In your case, until all the tenants are out, either voluntarily or by eviction, the unit is still occupied under claim of right, and it cannot be re-rented. The only part that the management company is wrong on is that you will simply have to pay the whole remaining 10 months. The landlord does have a duty to re-rent the property once it is vacant to end your obligation as soon as commercially reasonable.