OK, the good news is that if the house is not yours and you are not liable on the mortgage, you can walk away. You can find yourself a more appropriately sized apartment (ie 1 bedroom) or house to rent that you can afford under your own SS. If you can't afford to move because you don't have spare cash for a deposit (i.e. $500) you may want to consider holding onto your next months of benefits and NOT paying bills you can't afford so you can afford to move and pay that deposit. Just be sure to only rent what you know you can afford.
Another alternative is to bring in other trusted people to rent out of your mom's house - that way you can afford to pay the mortgage. If there are 3 bedrooms, for instance, and you only need 1, you can have two boarders. If you do this, I'd vet them appropriately, such as credit check, income check and criminal check. Charge the legal deposit amount to them, learn the eviction rules in advance so that IF you have to have someone removed, you can do so. Have a written 30 days lease, include in there firm rules. Consider having rent DUE on say the 1st, tack on $50 to what you want paid, but include an earl payment discount of $50 if they pay by the 25th of the prior month - it may provide incentive to pay early, which means NOT paying late. You can also have a late pay provision, but make sure it complies with any local laws on limits of such.
You indicate that you can't sell the house - this suggest to me that it is "under water" in that there is more owed on the mortgage than the house is actually worth. So you will either want to stay there because you can afford it with some tenants etc., or you will have to leave. It can take a very long time to get yourself removed by the bank once you stop paying the mortgage (which you are not liable for anyway, it seems) so that can buy you lots of months of saving if you hold on to your income and not use it to pay a mortgage that will fail anyway.