It's nothing for half the family to be unctuous (4)
I believe the answer is:
oily
'be unctuous' is the definition.
(I've seen this in another clue)
'it's nothing for half the family' is the wordplay.
'it's nothing' becomes 'O' (looks like zero - 0).
'for' is a charade indicator (letters next to each other).
'half the' suggests halving the letters.
'family' cut in half is 'ily'.
'o'+'ily'='OILY'
'to' acts as a link.
(Other definitions for oily that I've seen before include "covered in grease" , "Smooth; like lubricant" , "Oleaginous" , "Smarmy" , "Covered in lubricant" .)