Tenants Changing In Unit Security Deposit

[John K.]

Situation: Two adults, two children.  The two adults are parent and child (over 18), both are on the current lease.  They were inherited tenants, and have been EXCELLENT tenants almost always paying on time like clockwork and not having any issues.  

The child is moving out, and the parent was originally going to move.  We listed it - and now they want to stay.  Since winter is approaching we want to get them now on a 6 month lease to stay until spring.  

I want the lease to be in my format - so I don't want to just do a assignment or revision - I want just draft a new lease.  

Since the security deposit would be paid to both Parent and Child, and the parent is just staying - what kind of special language do I use to say that the security deposit is being transferred to new lease - but in addition when it is returned it will be made payable to "parent AND child" since they both submitted it?