When I made my earlier comments it wasn't clear that you had ALREADY consented to the 20 day extension for the removal of furniture from the house.
Common sense suggests that when somebody sells a house, they move out completely by close of escrow and convey the house to the buyer with nothing left in it or on the property. Though, as a buyer, I would make that clear in the purchase contract.
Seems to me that the only things the extension covers is the furniture in the house.
If there is anything other than furniture left behind by close of escrow, refuse to close and you'll see how fast they get their stuff (other than furniture) out of there.