Who pays my father's credit card debt after his death?

My mother is listed on the credit card statements along with my father. My mother has never used the card/account while my father has accrued over $20 000 in debt on this card. Her credit card number appears to be different, but I am worried that she will be held responsible for his debt upon his death because she is also on the statement. She never uses her credit card--is there any way to remove her name from the credit card account? Also, would I as his child be in any way responsible for paying his debt on all of his credit cards?