Also looking at M600s as strangely they are less popular than the M400s. Who knew.

Ok. Minor update.
Daughter No1 wants a 400/600 Supersport (and most likely a VFR400 or CBR400 track bike). Daughter No2 wants a 400/600 Monster.

I'd say that daughters wanting different road bikes would constitute a major update! Lol!

Looks like you need two bikes! Good thing you know a half decent mechanic, or it could get expensive maintaining two Ducatis 

One kid likes sport bikes and fast fours (WRX, Skylines) the other likes classic muscle cars and naked bikes. They're buying for their own tastes which is good. I'll supply the dirt bike for them to hone their skills and experiment with.
Its better this way, judging from how argue over borrowed clothes.