Is it permissible to perform the absentee funeral prayer (Salat al-Gha'ib) for a person whose death occurred a long time ago? Is it permissible to repeat the prayer for the same deceased person? And is it permissible to perform the prayer for multiple people while singling out one of them?

It is permissible to pray over the absent deceased, and it is not legislated to repeat the prayer over a single deceased person. It is preferable, according to some scholars, such as the Hanbalis and Malikis, to pray over multiple deceased individuals at once. It is also preferable for whoever prays over the deceased to intend to pray over all of them, though it is permissible if they intend to pray over a specific deceased person. However, if they intend to pray over a living person along with them, or omit some without specifying, or add to them after their initial intention, or intend to pray over some ambiguously and then some others similarly, or mention their number and they turn out to be more, the prayer is invalidated for all.