tenants handed in 1 months notice- need help with a few questions please

Tenancy Deposits

I recieved notice today that my tenants wish to leave the property. one has already moved out ant the other said they are moving out next week. there contract does not end until the 12th July. They will have paid all of there rent etc.

i have a few questions:

1. when we visited the property to fix the toilet we notice a large dent in the front pvc door. it looks like it has been done when moving furniture in. Do i need to retain part of the deposit? if so how much? the door obviously still does its job, but it is damaged.

2. Am I correct in thinking even though the tenants move out before the end of their agrrement, I can not let the property until the 13th July?

3. Do I have to also wait until the end of the tenancy agreement to return the deposit if necessary?

4. How do I retain proof that all bills etc have been paid in full?

5. I am on annual holiday next week when the tenant wants to move out, what should I do in regards to keys? should they put them through my door or keep hold of them until I go through the inventory with them again?

Sorry for all the questions! any help would be much appreciated.