Re duets: yet again, it all depends on what type of ballad you are talking about. I wouldn't think there'd be a big problem with stuff like 'The Golden Vanity', 'High Barbary' (or whatever it was that Child called it), 'The Mermaid' and some of the comic ones mentioned above. Many of their versions have tunes that suit quite a rhythmic approach, so the problem of synchronizing two voices is reduced. With the 'Big Boys', you generally need more vocal freedom to put them over, and to achieve vocal congruence between two singers would probably be to rehearse the life out of them. Also, the emotional involvement required for some big ballads is the kind of thing it's difficult to share. I wouldn't want to do 'False Foudrage' with someone else!

Sara Grey and Kieron Means do some ballads in close harmony - but they are, after all, mother and son, which gives them an advantage both in terms of phrasing and in their emotional bond.