How to close my deceased father in law's bank account?

I was a legal secretary for a while. An executor/execctrix is responsible for seeing that all of the deceased's final affairs are taken care of and that the will is followed. The best thing to do here is contact the attorney that issued the will. Most wills name an executor and perhaps this will already has one and that person needs to get the money out for you. If there was no will, contact an attorney who works with wills. This attorney will be able to answer all of your questions and best protect you from furture bills and further misunderstandings.