Well, I have 2 of them and they are grown up already(20 cm), they are living in 84 L tank. Question is can i but 2 young ones to live with them?? Do I need bigger tank and is that possible that older ones killing young ones???
Depending on how much younger they are I wouldn't recommend it- there is always the chance they might eat smaller ones.
Plus it's better to not overcrowd because they are very active so appreciate the space and if they become stressed then they may start eating eachothers gills etc.
I'd recommend keeping axies of the same size together if you have enough space and hiding places. smaller ones would be picked off by the adults, as you'll know they'll eat mostly anything small enough to fit in their mouths. Even when adults are housed together they will nip and bite each other's gills, although they will grow back it can cause stress.