Drama

My kids have been fighting over the same two toys for weeks now:

Yes, it's a bit odd that Jude is fighting Maddie to the death over princesses, but both Maddie and Jude are obsessed with them. When I asked Madelyn why she couldn't play with any of the other princesses (Jasmine, Snow White, etc) she told me that these two princesses were the only ones that could make a family. I told her that I didn't understand and she said, "Ariel is the mom, and sleeping beauty is the daughter." I showed her the other figurines and said that they could all do the same thing. She then said, "No, Ariel has to be the mom because she has the big boobs. Sleeping Beauty's are small-so she's just the little girl." She makes a good point. 
I then moved to Jude (who lovingly refers to the princesses as Oreo and Shake-a-booty). I tried to replace Ariel with Snow White, and he wasn't having it. He said that Oreo was pretty (must be the big boobs; have you seen her face?!) I then tried to take away Shake-a-booty, but he went berserk. I asked why she was so special, and he ran and grabbed Mr. Potato head. He then shoved Shake-a-booty into Mr. Potato head's butt, and began to shake Mr. Potato head like a maraca - dancing to the beat (Shake-a-booty explained).

Both children have very legit arguments. What's a mom to do?