Generally speaking once a person dies their debt dies with them. It is not inherited like china or tools are. However, since the lender has legal rights to be paid they can take the property. You might check and find out of there was death insurance on this loan. Sometimes there is.
I am not sure what you signed. If you signed the wrong papers *perhaps* you signed something that said you took posession of his debt. I would doubt it.
The other issue that could possibly mean your mom is able to be held liable for this debt is marriage. With marriage comes legal rights and responsibilities. It is possible she kept his part of the debt unless state law does not allow this.
To be safe, to be sure I would strongly suggest talking to a lawyer and losing a few hundred$$$ while doing it. It may be a lot cheaper to pay a lawyer than to be unrepresented.
If you are low income you may be able to find low income legal assistance ( for free). Check with the department of human services in your area. Also, you can ask your local and state representatives. They will know where to send you for help. Their phone number is listed in the book.
IF the summons says you need to appear at this date and time, yes, you need to appear at that day and time. It could be nothing more than an informal meeting to take care of this situation in a legally binding way under oath.... more
here are a couple of links that may help