I saw something on facebook about a set of twins. They both had 2 middle names, but instead of having 6 names between them, they each had a different combination of the same three names.
I think that's a horrible idea (what if one twin decides to go by her second middle name but she can't because it's her sister's first name? and why use 3 names when you could use 6?), so I'm changing it a little:
What if you had to name twins with 2 middle names each, but each name in one twin had to correspond to a related name in the other twin?
(Order doesn't matter, so you could use "___ Elizabeth ___" and "Isabella ___ ___". You can do one set of twins or try it for boy/boy, girl/girl, and boy/girl twins.)