Below is an excerpt from 

https://beachworks.org/2019/05/30/can-i-sell-my-house-if-behind-on-mortgage-payments/

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Can I Sell My House?

If you have just fallen behind on your mortgage payments and don’t have a way to make those payments for the foreseeable future, you may be able to sell your house quickly to get out of a pickle. In the current climate of the US housing market—and especially in Seattle where housing prices have gone up significantly in recent years—your house may be worth more than what you owe on the mortgage. However, this will depend on your individual situation and mortgage/refinance history. If your house is worth more than what you owe on the mortgage then you can sell it and use the profits to pay back the lender.

When selling property the traditional way, the escrow company will get a payoff amount from your lender and pay off the any existing mortgages at closing. This process looks largely the same when selling a house that is behind on payments—you will owe your lender what’s left on the mortgage plus any missed payments, interest and penalties.

In the event that your mortgage is more than what you could sell your house for, you may have to do a short sale, (a transaction in which your lender allows you to sell the house for less than what you owe on your mortgage). Lenders are not always eager to approve these kinds of transactions, but it is preferable to going through the foreclosure process.

Related Article: Seattle Housing Market Predictions 2019

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Reading this it's clear if a family wants to pay off their loan all that needs to happen is at closing when the title company asks us for the pay off the amount we send them the principal balance plus any past due amounts. after the sale is done nothing will be owed to the family. So nothing will stop the family from sellign the house them selling the house is the best thing they can do if they're behind.