as for the aba aba issue, aba's detect food by the electric signals from the prey. the aba should be smaller than the gator and pima, preferably 70% of their size and you give it a constant supply of live food. i dont think it will bother them. the logic is like this the aba aba wont go for the bigger fish because firstly there are other smaller target fish which its attention is focused on and since you give it a contant supply of food it wont try to eat the other bigger fish.
and in my observation in a tank where in there are bigger fish the aba dont roam too much it stays on one side as its territory and minds its own business.
about the gator provided the space is big, no food deficit and it is in a community tank since its small it should be ok.
pima's uhm pima pima pima no experience on pimas yet hehe!