I really really hope it was not Melafix in those jars, as Melafix can damage the labyrinth organs on Anabantoilds (the labyrinth organ is what they use to breathe air). 
Personally, I'd go ahead and acclimate them to your bigger tanks as soon as possible. I'm a big proponent of drip acclimation, which sounds like should work in this case.
IME bettas *usually* will do fine in large tanks, as long as they're with suitable tankmates (no other anabantoids, cichlids, or fish that will go after their fins like guppies and sometimes tetras). Occassionally you'll end up with a betta that seems to have the fishy form of agoraphobia, though, does not seem to be able to adapt to larger space and tankmates, or one that is too territorial with any tankmates, and needs to be kept in a smaller tank.
Personally, I'd go ahead and acclimate them to your bigger tanks as soon as possible. I'm a big proponent of drip acclimation, which sounds like should work in this case.
IME bettas *usually* will do fine in large tanks, as long as they're with suitable tankmates (no other anabantoids, cichlids, or fish that will go after their fins like guppies and sometimes tetras). Occassionally you'll end up with a betta that seems to have the fishy form of agoraphobia, though, does not seem to be able to adapt to larger space and tankmates, or one that is too territorial with any tankmates, and needs to be kept in a smaller tank.
