Poor guy, have you tried offering to buy the fish from your brother? Since you're doing all the care, the fish is basically yours anyway, so maybe you could go buy a critter keeper for him. They come in several size, and you can get a 2.5 gallon very cheap (like around 10 bucks cheap) at wal-mart. How old is your brother, is he even old enough to do proper care on his own?
My Current bettas:
Sullivan- Orange rose tail halfmoon male
Daisy- Mustard Gas (black and yellow) veil tail female
Milton- Teal butterfly halfmoon male (mom's betta)
DFTBA to nerdfighters working to decrease world suck!