Security Deposit Return Question

[Matthew R.]

Sort of an interesting problem, for me at least.  Hopefully it is a really easy answer and I am just overthinking it.

Rented out a unit to 3 people, A, B, and C.  They all signed the lease with a $700 security deposit required, which they gave me.  After a few months, C wanted to leave the unit.  C found someone to take over their room, D.  C was taken off the lease and D was added on.  Since the lease for the group was not over I did not return any of the security deposit.  During that time I received texts from C saying that D never paid them their portion of the security deposit.  A few months after that D decided they were going to leave, they made their intention clear with me, but did not tell their roommates I find out later.  She leaves and then asks to be taken off the lease, which I refuse to do because they did not find someone to take over their portion.  A and B are fine with paying the total rent for the last few months of the lease.  Now there lease is almost over, I suspect there are going to be some damages but probably not the full deposit amount.  Who and how do I return the security deposit to?  Just one check and I give it to A and B, or do I need to split the deposit three ways and send to A, B and D?

Thanks in advance.