When you die, then NO ONE inherits your debts.
But, any debts you owe, like medical bills, funeral, or credit cards must be paid with (your) assets that you have when you die. Now if there is (not) enough to pay your bills, then the creditors will get what you have or (nothing), but your nieces will also get nothing, since there is nothing to collect.
Put simply, debts paid from assets, then (if) any assets left over go to your nieces.
The only way around it, if you think your debts won't be covered when you die, is to get life insurance and have your nieces beneficiaries. With life insurance is (outside) probate, thus (anyone) who is the beneficiary gets paid and can use the money for (what) they want.