First of all: Welcome to MFK!
If they get too big, another solution would be to eat the fish yourself, or give them to someone who eats them.
Sounds cruel, but these fish are eaten in other parts of the world.
I know it's difficult to eat fish you raised yourself, but I think it's better to eat them than to let them suffer a life as stunted predator in a far too small tank..
I might get some hate for this, but... well, I'm just saying what I think.
But, as you were told before, it is always better to do dome research on the animals you want, before you buy them.