Sadly sergeant and daughter becoming alienated (9)
I believe the answer is:
estranged
'alienated' is the definition.
(I know that alienated can be written as estranged)
'sadly sergeant and daughter' is the wordplay.
'sadly' indicates an anagram.
'and' is a charade indicator (letters next to each other).
'daughter' becomes 'd' (genealogical abbreviation).
'sergeant' with letters rearranged gives 'estrange'.
'estrange'+'d'='ESTRANGED'
'becoming' acts as a link.
(Other definitions for estranged that I've seen before include "Sad regent (anag) - disaffected" , "Cut off" , "no longer friendly" , "Having become unfriendly or alienated" , "Alienated, disaffected" .)