1, jacks all soem a several distinctive moves, and each of their stratagy evolve around these unique moves.
g.jack has d+4 with comes with some tag combos starters, his b+2, b+1+2 given him some defensive tictac, his d/b+1 is the best, and he has the best throw mixups in the game,(yes better than king).
jack2 is has the best oki game and pressure game with ff+3 and b+3+4(or d+3+4? the should smash), possibly the best jack.
p.jack's game evolves his ss and d+1+2 stagger.
2, the reason to have all thse jacks is that they are disadvantaged againest other chars, if you want have a fair game of jack vs jack, u have to team jack with a jack, so namco give you 3 jacks to choose from.
because the "team up" nature of TTT, their similarities dont matter. as far as i am concerned, their similarity is a lot less than ryu/ken/akuma/sakura/dan