Fairy-tale siblings (6,3,6)
I believe the answer is:
hansel and gretel
'fairy-tale siblings' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hansel and gretel that I've seen before include "children abandoned in forest" , "Fairy story" , "fairy tale" , "18 [OPERA]" , "Witch-killing pair" .)