There is is no such thing as a de facto owner of the rights. Either a person owns the rights or they don’t. It would likely require a court to order the transfer of the rights if the parents wish to claim them. For all we know the videos have financial value and the decedent has debts which would require the sale of,the rights in an effort to pay estate debts.
The legal owner of the rights can send dmca takedown notIces to any service publishing the videos. If the service,refuses to comply or puts the videos back up after complying with the law and the person posting the video claims a right to post the video, the owner can take legal action to have them removed if they choose to do so.