Their only form of income is thru social security and that's it. They do have one checking account where the social security is automatically deposited.
It's something of an unrelated point, but I have to wonder about your father living overseas. You said your mother is living with your sister. I assume that's rent free. How is your father paying his living expenses? As someone who has done collection work in the past, I can tell you that the facts you have told us so far will raise questions about your claim that they have no non-exempt income or assets.
The summons for both my mother and father was left at the door. My mother speaks very little english and she said someone came to the door asking for someone and she said to the person in broken english saying she doesn't understand. And the person then left 2 copies of the summons at the door.
I'm not sure why the process server wouldn't have handed her the summons and complaint. That's probably proper service as to your mother. Not likely for your father since he doesn't appear to live there anymore.
My parents only have a few hundred dollars to their names and that's why my mom is not able to pay the credit cards.
Then she shouldn't be using them. If she is still using credit cards knowing she has no ability to pay them, that's fraud. If these are old debts, then that shouldn't be an issue.
At this point, would filing bankruptcy be an option? and can she file bankruptcy without my father there?
Bankruptcy is an option, but the question is whether it is worthwhile. If your parents have no non-exempt income or assets, then what they do have is already protected, so bankruptcy protection doesn't serve any real purpose. Your mother could file on her own or jointly with your father. If your father is part of it, then he will need to return at least once for an examination in court.