I presume they'd all be humble enough to sit on the floor & leave the chair unoccupied....or maybe take turns in the chair.
Had these "people" ever really existed I reckon they'd have been fair enough to work it out amicably....it's the idiots that have followed on in their footsteps that have tainted the whole picture since.
Jesus would make enough chairs for everyone and sit on the floor....dur.
They (the prophets) will all stand in the room, just looking at the chair, saying nothing.
Then all the followers of those religions will fight and kill each others screaming that their prophet should be sitting in the chair because it's god's will....
Some followers will not claim anything at all because they dont like violence but they'll be killed anyway, just in case they start to have ideas....