I'm just asking out of curiosity. I don't have any plans to actually use a three of one pet team. Seems like it wouldn't be very balanced. But, just for fun, I have been using a three Squashling team just because of my name. It's not for any serious battling. I think the highest level on is 4.
Would be interesting to hear if anyone has a serious team that's doing well with three of the same pet.