my husbands mom died before receiving a settlement it was in her will to be split between her sons received 1 payment then 1 son died now what

If the mother in law died in Illinois, then a probate proceeding would be required for her estate in Illinois. Any inheritance from the mother's estate would be paid to the estate of her son. If the son lived in California, then depending on the type and amount of his property, including the inheritance from the mother, would determine what type of probate proceeding is required in California for the son.