Question

We flew abroad and left the house to friends.
The house locks from the outside without a key, so if you forget the key inside, you can’t get in.
We left a key with the neighbor.
The neighbor is a somewhat older and rather strict person, but specifically with us we got along well.
The friends who were in the house live on a kibbutz; they have no habit at all of taking the key.
Within three days, four times they asked him for the key.
 
The fourth time he got angry and said he wouldn’t bring it to them and that they should stay outside.
 
After an hour he brought it to them.
 
In my opinion he behaved fine, and they really were pretty careless.
 
But the halakhic question interests me.
 
Is he obligated to bring it to them immediately because he is like an unpaid watchman or an unpaid worker who undertook to bring it whenever they asked?
 
Obviously, the third time he could have told them: take the key and don’t give it back to me; I’m no longer interested.
 
But as long as the key is with him, maybe he isn’t allowed to try to educate them, and first of all he should do what he undertook to do.