As a general practice, keys should not be given until monies have been conveyed. The closing attorney or title office will often times hold the keys as a matter of convenience and then will contact all parties once funds have been transferred.
I had a house not close that I was selling and the people moved in. My seller went to check on it over the weekend...their financing fell through. I called the buyer's agent who gave them a key at the walkthrough...no answer. It was a Friday and it eventually closed on Tuesday. The people called me personally to make sure when it finally did.
Technically, the buyer should not take possession of the keys/house until the deed is on record. However, it is quite customary to give the keys to either the buyer's attorney or agent. Technically, the house is not theirs until it goes on record.
I believe yes you should. However this is a matter of personal opinion. The real answer is NO the sellers do not have to because they have not received the funds yet. Builders in particular can be sticklers on this because wires can be called back and deals have fallen through even last second at the table (this is extremely rare). Best solution is to have the closing scheduled for a time you know funds will be there. This avoids the situation all together. Hope this helps