Hopefully you purchased the home with a professional real estate agent. They can go to the contract and the terms should have been in the contract asking for say $100 per day as damages. The title company should hold the check to the sellers until the situation is rectified.If you bought directly as a FSBO then you must go by the terms of the agreement that you signed.This ultimately is a legal question and should be answered by a legal professional.
Closing costs vary from state to state and from type of loan along with the terms of the purchase agreement. You will need to check with your Real Estate Agent or lending institution to get the amount.
The lender has no control over what the appraisal comes in at. The appraisal normally comes in at what the purchase agreement amount or maybe a few thousand above, but usually not more than that in that the appraiser knows what the home was listed for and possibly even the selling price. The sales price being a fair and honest price in an arms length transaction is what the bank is looking for and that should be the purchase amount. If it comes in less, the bank will still loan, butt you will have to pay the difference. If it comes in more, the bank bases the loan on the lowest of the purchase price or appraisal.
Everyone's situation is different. In today's market and stricter laws for loans you will first need to check with your bank or mortgage broker to see if you qualify and also to see if they will provide you a swing loan.
Legal questions of which this definitely falls under should be asked of individuals who are licensed to practice law. They can read the contract and advise you of your options.
You need to use your agent as that keeps everything and everybody on the same page and legal. You also need to keep in mind that if it is not in writing, then it didn't happen.
Have you asked the FSBO if they would pay a brokers fee to a Real Estate Agent? It is in your best interests to use a professional, but it appears that you should talk with another agent about the situation and see if they will help.
Was this home appraised by your lender? If so, the lender will not pay over the appraised price when figuring out your loan. Any amounts over the appraised would be your responsibility at 100%.. You can ask the lender to have another appraisal or talk with the loan officer to see if they have any suggestions. The SELLER will not be able to find a buyer for the home to pay over any appraised values so your REALTOR should be able to negotiate this situation for you.