This amazes me...a kid goes to camp and a mom can't feed his fish?
Will she feed them twice a week while you are gone?...even once/week and you'll have over 90% survive. I used to raise Bettas for store credit(mostly) back in the 1970's.
The local Mont-ala bar provided me with all the used paper cups I could get out of there trash cans for the males. As long as I kept a betta wet it lived to die of old age.
I'd leave the fish where they are and not waste all that money on an unproven system. Your losses will be less if they stay where they are and your "mom" feeds them once a week...
Do you go out and harvest mosquito larva? Is that her issue... certainly dropping a few flakes/pellets of food in each container every couple of days isn't too demanding on her schedule? Perhaps you can pay her? (Does that sound as odd to you as it does to me?)
"Those aren't poodles. They're Dobermans with afros."