Why do you need time? The reverse mortgages has to be paid off. You have had a year. If you want the house for yourself, you should payoff the mortgage.
HECM borrowers do not have to repay the HECM loan until the borrowers no longer use the home as their principal residence or fail to meet the obligations of the mortgage.
When the home is sold or no longer used as a primary residence, the cash, interest, and other HECM finance charges must be repaid. All proceeds beyond the amount owed belong to your spouse or estate.
If there is no money left, there is no money left. But you know all this, so what is the question?
Have you rented it out? Are you living in it? I don't have any experience, but my expectation is that this is not a normal foreclosure. There is no hope that your grandmother will be able to pay them back. Maybe you can, but then you should do it. Or are you trying to sell it on your own, but have not been successful?
It sounds like a hassle to me. Since the loan is greater than the value, give them the keys. What is stopping you? I feel some details are missing.
I don't think they can ask for a deficiency judgment against you, so it wouldn't matter if they were selling it for only 80% of current value. Actually, if they sold it for 80% of current value, that would make it easier for you to buy if you want it.