Hi and welcome to the forum if we hadn't met before - If we did and I forgot, welcome back
As rainbow shark you mean the black one with the orange fins aka Epalzeorhynchos frenatum
Considering its adult size of 6" even a 55g is going to cut it short on him as adult, they're commonly housed in a 70g. So def move him out of the 29g now that you have the opportunity.
Bala's aka Balantiocheilos melanopterus
will grow you to 14-16" so uhm yea neeedless to say they're way past keeping in 55g, more like 200+g so I'd either place them on aquabid or see if your LFS is interested.
Then once that's sorted out, I'd go through all you have in your 29g and sort them out by their needs between the 55 and 29g and then add additional stock thereafter.