Terms for letting tenants out of lease?

[Anna Watkins]

Tenants who moved in with a 12-month lease in April sent an email today saying a parent is buying them a house, it happened quickly, and they will be moving out September 1, only 4 months into the lease.  They've been good tenants, if young and slightly needy, and after growling and kicking doors I calmed down to think about terms.  The lease does NOT include an early exit clause (how did that happen? no idea and need to edit the lease for next time). The lease does stipulate that if they don't want to renew a lease, or want to leave after going month-to-month at the end of a lease, they need to give 60 days notice.  As it stands they're giving me 30 days. 

 The house is in unincorporated Decatur, Ga, a relatively popular intown area of Atlanta and probably won't be too hard to get new tenants (but what a pain)

I've  come up with these terms -- please give feedback --

I'll release them from the contract if we all agree in writing that:

1) they understand that they're breaking a  binding contract and legally they are responsible for the remaining 7 months of rent, HOWEVER

2) they are responsible for paying the rent in September, since they're not giving 60 days notice, BUT if a new tenant lease begins before October 1, I'll refund what they paid for September prorated for the days covered by a new lease.

3) I get to show the house to prospectives before September 1,

4) any costs incurred in getting the house ready for the next tenants will come out of the security deposit.

Does this sound reasonable?  Or should I just keep the security deposits and let them go? Is this legal in Georgia?

I haven't checked the Georgia Tenant-Landlord handbook to see if/what it says about this.

Thanks for your ideas on solving this situation.