Legal Question in Credit and Debt Law in Pennsylvania

I'm afraid this is a question of estate law. I'd resubmit it as such.

You need to see a probate attorney in the county/state where your mother lived at the time of her death. Claims have to be paid in order of priority if there are not enough assets in the estate. You do not reveal enough information as to whether there are enough assets to pay this claim. I also do not know whether this pension check is higher in priority than the medical bills or not. If not and all assets of the estate are exhausted, then the pension fund has to eat it. If the pension is higher in priority, then the medical people will have to refund the money - which is not going to happen. However, if there are no assets, then nothing can be done by the pension - you and your siblings are not going to be personally responsible unless there are assets in the estate.