What is the ruling on performing 'Umrah or Hajj on behalf of one's grandfather, grandmother, or another person other than one's parents, regardless of whether they have already performed the obligatory Hajj or not?

Hajj and Umrah on behalf of another are permissible in two instances: for the deceased, and for the physically incapacitated person who is unable to perform it himself, whether it is an obligatory Hajj or a voluntary one, according to the preponderant opinion. The condition for this is that the proxy must have already performed Hajj for himself. Some scholars permit deputizing for a person who is physically able to perform voluntary Hajj, while many others forbid deputizing for a physically able person in voluntary Hajj, just as in obligatory Hajj. Based on this, it is permissible to perform Hajj on behalf of grandparents if they are deceased or physically incapacitated and unable to perform Hajj themselves.