a PF campaign I run have 3 players, and an occassional 4th
TBH they are having no problems with low numbers as the characters have so much more options now. If for example someone takes the 'rich' trait, they can start off with a few MW items each and a WOCL
as long as you have fighter or paladin, a cleric and a wiz or sor....you dont need a rogue and you just have to be creative in the wilderness bits of adventures.
the party i run with are all EVIL so dont have a spontaneous CLW caster. they are a barbarian, a cleric and a sorceror.
they can all do lots. a Gestalt of some classes would just be a horrid character sheet loaded with abilities.
you could just give them all say max hp for the first two levels and an extra 2 skill points and id bet they be fine w/o going Gestalt.