Q: My lessee took in two roommates.  They left and my lessee took on two replacements who now also want to leave.  The problem is that the roommates say they contributed to the security deposit and that they want their share back.  The place is in a mess, which the roommates say was there when they arrived.  What do I do?

Stay out of it!  The cardinal rule in a multi-tenant situation is to name only one person as the lessee, and to accept money from only that one person.   While the lease may allow the lessee to take in roommates (or you may be required by Berkeley law to let him/her to that), you want to look to only one person for payment of deposits, and you want to be responsible to only one person when the tenancy ends.  An incidental benefit from following this cardinal rule is that once your named lessee moves, you may reset the rent to market for the stay-behinds.

And before you let your lessee into the place be sure there has been a pre-occupancy inspection verifying the presence (or absence) of any damages (or pre-existing “messes”) that might give rise to a dispute over the deposit.  This should be acknowledged in the lease.