Lease splitting question - how to handle

[Stephanie M.]

We have a 2 bedroom unit renting month to month, 2 tenants that are friends in the unit, total rent $1060/mo. Tenant #1 just gave their 30 day notice, she will be moving out of the unit May 9th. The other tenant #2 wants to stay. What is the proper way to word the new lease moving forward and handling prorated rent? This is my train of thought:

Prorated rent for the tenant #1 moving out : $153.87 due May 1st, for move out on May 9th.

Prorated rent due on May 1st $906 for tenant #2 wishing to stay, will continue month to month. June 1st rent for this tenant will be $1060/mo.

Questions: When do we do the walk through for Tenant #1 security deposit? Right after Tenant #1 leaves, even though #2 is still living there? When does the security deposit get returned for tenant #1? How to verbalize that Tenant #2 owes full rent moving forward. The new lease for Tenant #2 would begin May 1st or June 1st?? THANK YOU FOR ANY SUGGESTIONS!