Wise specialist mostly sorted out niece and daughter (11)
I believe the answer is:
experienced
'wise' is the definition.
(thesaurus)
'specialist mostly sorted out niece and daughter' is the wordplay.
'specialist' becomes 'expert' (I've seen this before).
'mostly' means to remove the last letter.
'sorted out' indicates an anagram.
'and' is a charade indicator (letters next to each other).
'daughter' becomes 'd' (genealogical abbreviation).
'expert' with its last letter taken off is 'exper'.
'niece' anagrammed gives 'ience'.
'exper'+'ience'+'d'='EXPERIENCED'
(Other definitions for experienced that I've seen before include "went through" , "Practised and knowledgeable" , "Having much accumulated knowledge" , "Practised, well-versed" , "No novice" .)