1/3 tenants moving out. Sign new lease? Security deposit?

[Sammy Msouty]

We originally had 3 people sign a year lease. We've only taken payment from tenant A the entire year, including the original security deposit. 

Tenant A is now leaving but Tenants B and C want to renew with a Tenant D (a person they found). 

Do I give Tenant A the entire security deposit back and then charge Tenants B, C, and D another security deposit? If so, should I do a full inspection and subtract damages from the deposit amount? Also, is it reasonable to ask for the 2nd security deposit before I refund the first one?

Or, should I simply state the deposit remains since only one of the original 3 tenants is leaving and say that they have to figure it out from there (e.g. Tenant D pays his share to Tenant A). Would I be legally vulnerable since it was Tenant A who actually made all of the payments on behalf of Tenants B and C?

Thank you!