Sure, no problem. I'm always glad to help.
So your brother's bettas aren't in Aqua Boxes? Otherwise I'd say it was the sand. By the way, I know the website says to change the water only once a month but I guarantee your bettas will get very sick and die from ammonia poisoning if you don't change the water at least once a day.
And uhm, actually *a bit embarassed* the Aqua Boxes are currently the target of a hate thread right now so they're not popular at all. But if you change the water very frequently, then your bettas will probably be okay. My main concern is the buildup of ammonia. Uhm, it's nothing personal, really. ^_^ No one knew there was a responsible betta owner who did keep their betta in one. We're all mad about the irresponsible
What are your bettas' names and what colors are they? Can you post pics? We always love to see pics of bettas.