The first superior appointed was Fr Schmidberger. Mgr. Lefebvre was against the idea of having one of the bishops as superior as he feared it would place one of them over the other three, which would not be correct as all 4 were of equal standing. Mgr Lefebvre was proved to be right. +Fellay should never have been appointed afterward. It was a sad mistake by the Society, as we now witness.
Also their position was more specifically for the ordination of deacons and priests, to ensure the continuity of the priesthood in the SSPX, and also to administer the sacrament of Confirmation.
Yes, ABL consecrated 4 bishops to provide the Society with enough episcopal
versatility to give the traditional sacraments to the world, as the demand at that time
seemed to ask for. Again, his overriding concern was to avoid any appearance of a
parallel Church, or a permanent alternative to Roman Catholic. "We are Roman
Catholic" could have been his motto.
I must admit I do not know how +Fellay came to be appointed and why he stood. I also very much believe that another mistake by the Society was to elect any of them for such a long period of 12 yrs; I don't think it was even necessary from an admin point of view.
The election of the SG in the SSPX is not a publicly reported process. It is rather
shrouded in secrecy, something like a papal conclave. We saw just two weeks ago
how sequestered the GC was: that's nothing new. As for the 12 years, that is the
term that ABL put into the rules for the Society. Some have said that he didn't
expect this problem of Rome going off the rails to endure much more than 12 years.
We are now thinking that 12 years was a mistake, and it was also a mistake to not
put into the rules that a bishop could not be elected SG, and it was especially a
mistake to not put into the rules that a bishop couldn't be RE-ELECTED SG. Imagine,
if ABL had done any of those things, +Fellay would not have had this destructive
power trip going on today.