Legal Question in Real Estate Law in California

First, look to see whether the lease makes all tenants "jointly and severally" liable for lease payments, fees, etc. "Joint and several" liability means that the landlord can collect as he/she/it chooses -- either equally from each of the four of you, or 100% from you alone, or whatever. That will determine the apportionment between the landlord and the tenants. Then, there's the question of how any liability would be divided amongst the four of you, i.e., your rights against each other, rather than the landlord's rights. That question would probably be determined, if it went to court, by a "whatever is fair" kind of standard -- in other words, the tenant that caused the lease to be "broken" would probably get stuck with any losses and penalties that the landlord was able to impose. However, be careful to note that (a) there are two separate liability-allocation issues here, one involving the landlord and the other not; and (b) the contract or contracts involved may call for a different result, so review them carefully.