How far upside down are they on the car? See if you can sell it, then pay the difference with either cash or a small loan. Can your mom get a part time job at Walmart or something else? If they sell their house, how much will they have from the sale? Could they stay with you for a few months until they found a smaller house to live in? Can they sell the older car and use that to pay the difference in what they owe to the new car? They could then turn around and get a cheap beater for the both of them since your mom is not working. Sorry to hear about this, my wife's parents are in it up to their eyeballs with medical debt and her mom can't work because of her back.
Sold my 2006 dually.
2011 GMC Sierra Denali now with 6.2.