I’d be interested to get a feel for how often inversion is used in everyday speech and the register of the examples below, from further down the thread. Presumably the one with quand at the end is the least formal?
Quand Juliette et Pauline ont-elles déménagé ?
Juliette et Pauline, quand ont-elles déménagé ?
Juliette et Pauline, elles ont déménagé quand ?