@Brian Zaug If the remaining tenant's income qualifies, let her fulfill the lease on her own. You mentioned 3 kids, which sometimes challenges the move-in conditions. Why not have a move out inspection on Monday? See if the adults need to pay for any damages or repairs that arose since move-in. The guy leaving is responsible for half of any repair charges and should be paid for now.
After inspection, you can talk about security deposit. What does the lease say? Mine says that the security deposit will be held until all parties vacate and will be returned according to the law. If your records show that they each wrote a check for half and no repairs charges are immanent, the departing person may be owed money IN AUGUST.
Amend the lease original with a one page Addendum. 'This Addendum is made by and between X (Landlord) and X and X (Tenants) made on (date of the original lease agreement) for the property located at (give dwelling address). The LL and Tenants agree to amend the Lease Agreement. The LL and Tenants agree that X may be released from all obligations of the lease signed on (name the date of the original). X will no longer be responsible for rent or damages from this date forward. X will be solely responsible for monthly rent and charges that may arise from renting the property at (give address). The security deposit will remain with the LL until all parties vacate the premises and will be refunded according to the law. All other terms of the rental agreement remain unchanged.' All parties of the original lease must sign the Addendum.
In July, inspect again (3 kids) and decide if you want to amend the term for another year, or not. Repair charges must be paid in full, along with signing the renewal, for the new term that begins Aug 1, 2022.