Your aunt may have to call an estate lawyer. If your cousin was named the executor in the will. He may have grounds to name someone else on his behalf, since I don't think he is allowed to conduct work in prison. Or possibly, the courts may have to assign someone to be executor of the estate.
Wills don't actually name someone as executor; they nominate someone, and then the Court has to accept that person as executor. If the Court finds a person is not competent to be executor, because of mental illness, health, inability, unwillingness, or possibly criminal record, the Court can refuse to allow that person to be the executor.
Since the son is in prison (not jail, prison) for the rest of his life, the son is not eligible to be executor. He won't be able to arrange the things that need to be done, since he can't leave the prison, so how would the son even get the paperwork processed? Since he's in prison for the rest of his life, he committed a major felony which would disqualify him.
Was the will prepared before the son went to prison? I hope the father had a competent lawyer prepare the will. Perhaps the father nominated his son out of love with the full knowledge that the son couldn't perform the job, but he wanted to do so to let his son know he still loved him.
Was a standby executor nominated in the will in the event the first person nominated was ineligible? The son isn't going to be able to name someone else as standby executor although he can definitely suggest to his aunt that she go file for probate of the estate. Any interested person can file for probate, and then the Court will determine if that person or someone else will be the executor.
Oh, and to answer the question in the subject, no prisoners don't have all their Constitutional rights. Quite a few of them were taken away when they were convicted and subsequently sentenced.
