Relatives requiring new compositions without piano (6)
I believe the answer is:
nieces
'relatives' is the definition.
(niece is a kind of relative)
'new compositions without piano' is the wordplay.
'new' becomes 'n'.
'compositions' becomes 'pieces' ('piece' can be a synonym of 'composition').
'without' indicates named letters should be taken away.
'piano' becomes 'p'.
'pieces' with 'p' removed is 'ieces'.
'n'+'ieces'='NIECES'
'requiring' acts as a link.
(Other definitions for nieces that I've seen before include "They're related" , "Scene I set up for relatives" , "Relations" , "Relatives of 27dn" , "Young female relatives" .)