As a general rule of thumb ,Ive found that its a very good idea to keep them fairly close to the same size . Cresteds are amazingly hardy animals but the one thing they dont respound well to is stress .This includes bullies in thier cage.
Often times the first sign is the end up losing thier tail ,not life threatening but most of us prefer them to keep it on.
Second sign is they begin to lose weight ,While Ive never played it out to the end Im sure the final step is death.
I have found even males can be bullied by females .Once a animal bullies another it seems to be forever ,even seperating them until sizes equal up results in a bullied animal once placed back in the cage.
Your far better off waiting until your two females catch up to the third in size which should result in a better beginning for all of them.
Also while I dont know for a fact it is necesarry when you introduce them I tend to change the cage around so that no one feels they have a territory that is being invaded.

Slizards.com