Tubs are a great idea if humidity will be a problem and those normal measures don't get the job done.

It's not recommended to keep more than one in a single enclosure for several reasons. You run the risk of cannibalism (extremely rare, but real), and if one gets sick and has a regurge or some sort of odd stool it can be impossible to tell which. There's disease transmission, but if you're getting them from the same place that's probably not an issue. If they are a m/f pair, you run the risk of premature breeding which could seriously endanger your female's life.

You can divide the big tank with some sort of sealable, nonporous material like glass, plexiglass, any plastic, really. If they're hatchlings, a 50 or even half that will be HUGE to them.

I really do recommend small tubs (like, 16qt) as a solution to all your possible problems. Good luck and make sure you have a thermostat!