Hardship of a daughter, and son, in truth (9)
I believe the answer is:
adversity
'hardship' is the definition.
('adversity' can be a synonym of 'hardship')
'a daughter and son in truth' is the wordplay.
'a daughter' becomes 'ad' (I've seen this in other clues).
'and' means one lot of letters go next to another.
'son' becomes 's'.
'in' is an insertion indicator.
'truth' becomes 'verity' (verity is a kind of truth**).
's' placed within 'verity' is 'versity'.
'ad'+'versity'='ADVERSITY'
'of' is the link.
(Other definitions for adversity that I've seen before include "Circumstances that cause trouble or sorrow" , "Misfortune, hardship" , "Hard times or misfortune" , "State of misfortune or affliction" .)