I as understand it (again, ask a lawyer) you are under no obligation to serve as executor just because you were chosen by your parents in the will. You can simply decline.
Also, heirs have no personal responsibility to pay debts of the decedent. If the estate can't pay the debts, the creditors simply lose. They can't make you pay it out of your pocket.
For that matter, you could simply make your wishes known to your parents, and ask them to designate a different executor and/or delete you as an heir (and just leave everything to your sister, or whoever else they want to have it).