I'm thinking I should amend my 1040 but I don't know what strategy to take.I made about $35k in interest from installment sales in 2010 and $18k in principle payments on the sales.I never file Schedule A.What should I do???

I would DEFINITELY renegotiate and sign an amendment to the current lease switching it to a month to month lease before listing the house for sale, which can be cancelled by you with 30 days notice.

I told her I had not and mentioned the reasons (above); I had not received an amended contract or an answer about the $1000 down.

Any amendment to the contract has to be in writing and agreed to by the Vendee.

He asks to look at my contract, which I give him along with my assignment paperwork, disclosures, and an amendment I used to adjust the original price on the purchase contract.After a day he gets back to me stating that his "attorney has advised that he make the offer to the seller and leave the name blank on the contract with his desired terms".  

Shopping for another loan this late in the game is not going to be an option unless you can amend the purchase contract to push out the closing.

The only thing you should amend is with the closing cost credits.

The title company then sent us an amended report with the lien removed.

I would like to pay back $66,666.66 so that I can have an amended return filed for 2020 and not pay the taxes due on the 2nd installment for 2021. 

You can go back and amend prior years to show the income.