Being sued by previous car lender

issues. In 9/16, grandma cosigned a car for me. She had passed on 1/17. No probabte has been opened due to no funds upfront,& other heirs wont help. I had ankle surgery on 12/17, was off for 2 months, got behind on car payment. I got caught back up as good as I could. In 6/18, I had to quit my job. On 7/18, the car was repossessed. I now got letter saying I am being sued. Can they open probabte for her portion? I have no where else to live. Mother lives with boyfriend in another state in a 1 bedroom apt both on disability. Brother/sister law just sold their house and lives in an apt in another state as well. I know I can file chapter 7 or 13, but if I file chapter 13, can they still open probabte and force to sell and force me to be homeless?