1. 如果房客breach lease, usually there will be a reletting fee due immediately. (check your lease).
2. Tenants are responsible for the rent and utility until the new tenants move-in.
3. Landlord can not charge double rent, so he has to refund the prorated rent after new tenants moved in.
4. The rental market is so hot now in dallas austin area, I am pretty sure they can find the new tenants if you cooperate with the showing.
5. Everything is negotiable, if I were your landlord and you agreed to cooperate with the showing. I will be pretty happy with your offer.