Addressing the possibility of an alliance of 5 going through, there is a slim chance but nevertheless a possibility and a chance that it can happen.
We had 4 tribes of 5 in Survivor: Cook Islands, but they switched them to 2 tribes in Episode three, which was kind of a bummer to me because I would have rather seen all 4 tribes go all the way to the merge without a switch!
I know right! Or at least they could have whittled it down to three tribes of six instead perhaps. A pity really, because I saw photos that showed one of the challenges that had been prepared for all four tribes to play. The one with the evacuee, where they had to bring the stretcher out to a person cuffed to a structure in the sea. Oh well...