For feeding reasons it's best to house each separately.
Depending on where you live, the sweater boxes may hold in much needed humidity and warmth that is more difficult in an aquarium.
Small adults can be kept in Rubbermaid’s model 2221 which is 5.853 x 16.825 x 23 in.
I'm not sure which Rubbermaid you are calling 96 quart but somewhere (maybe Sterilite's site) I found one and it was over 12" tall. If you are only going to make a 4 tall rack this is probably ok but you don't necessarily need that much height.
On Rubbermaid's site I found the following model numbers and dimensions:
2141
9 x 39 x 16.25 in
2267-87
10.602 x 33.38 x 20.782 in
2159
6.231 x 34 x 16.442 in
I'm not sure where these can actually be found in stores and I wouldn't be surprised if there are other models not listed. I think any of these would be good for even very large adults, I especially like the 9 and 10 inch tall ones.
Just looking at the pictures though I’m not sure what the bottoms look like. You’ll want to look for ones with as flat of bottoms as possible to make them easier to whip out when cleaning.