Hi! Welcome to the forum. I went looking for this the other day, and now it's coming in handy again: here is a basic care sheet for most species of toad by John P. Clare, the administrator and owner of this site:
http://www.frogforum.net/content.php...ytes-Pelobates
While the guide covers substrate, sand isn't a good substrate. A pure substrate of Coco fiber is usually the best option, and is available in brick form under a number of brands. I find the best(cheapest) retailer to get it at is Pet food Express, at 2.50 a brick versus as much as 6 at some retailers. Often a bulk deal online is even better.
Considering your sterilite bin, I personally would suggest you pick up a 90 qt bin, as they are pretty cheap(8$+tax near me.), as it will give the three of them more room to move around. Really, you can keep these toads permanently if you like. Most Toads burrow and wait out winter, basically hibernating, but I believe I've read young toads have lower survival rate than adults. They can tolerate temperatures as low as 60°f(I personally prefer to keep them around 65 at the coldest), so as long as your room(or whatever room you're going to keep them in) doesn't get too cold you can keep them comfortable year round. If it does get too cold, a heating pad or low wattage heat lamp should do the trick. If you have any more concerns, please don't hesitate to ask! I hope this helps.
Edit: I would suggest crickets or dubia Roaches over mealworms. Mealworms contain a lot of chitin/shell.