Boy, I tell you the Frozen thing has been really fun to hear about. I have a colleague whose great granddaughter was absolutely in a state of distress because her sister was going to be Elsa and consequently told her she could not. You teach to that just as you do name calling or hitting or any other sibling fighting. The truth of the matter is that first of all an apology is owed and an apology will be received. Second of all, it is perfectly fine for both of you to be Elsa or both of you to be Anna or we will get the costumes and you can decide and you can be whoever you want to be. That is a really good message to send to kids.
Get a chuckle out of it and don't panic too much and laugh over the fact that in probably ten years when they are 15 or 17, whatever the ages are, they would die a thousand deaths if they went out of the house wearing the same outfit. So this too will pass so just don't panic over it too much. Teach to it and keep moving on.
