A power of attorney has no effect on what happens after a person dies; the POA expires when the person expires, and POAs only apply to still-living people. If there is a will, then whomever the will indicates becomes the executor. If there is no will, then the court (i.e. probate court; sometimes called surrogate's court) will have to appoint someone the "administrator" or "personal representative" of the estate--this person will have the same powers as an executor. It will generally be a spouse, if there is a living one; or if not, it will be a child, often the oldest (especially if the other children do not object to that person's appointment). If the oldest child wants this role, he should contact the court, explain that his father died without a will, and ask for directions and instructions to be appointed administrator/personal representative.