Not enough information, since there is no indication whether this is a deeded ownership or some form of points / club membership. If it’s deeded ownership, a new deed will need to be prepared and recorded to lawfully effect an ownership transfer. If it’s a points / club membership of some kind, contact Vistana to find out their internal procedures for transfer. In either case, please first make very sure that your son actually wants this particular new financial responsibility and burden at all in the first place.
KC