Thank you! I saw the pic of your new girl and I have to agree she looks fairly similar to Mew!
As for my girls, they get along just fine, now that I've removed the one that starts all the fights temporarily. They swim around together a lot.. The worst of it is maybe flaring and a bit of chasing. And they can get pretty crazy during feeding time but otherwise they usually get along.
As for my PK girls, size doesn't seem to matter a bit. That was the main thing i was afraid of when I put them together, but my 2nd smallest fish has overpowered my biggest quite a few times!
It all depends on the fish's personality though. Best of luck with your sorority!