Posers, twin daughters thrown in nettles (7)
I believe the answer is:
riddles
'posers' is the definition.
(I've seen this in another clue)
'twin daughters thrown in nettles' is the wordplay.
'twin daughters' means two substitutions for 'daughters'.
'daughters' becomes 'd' (genealogical abbreviation for daughters).
'daughters' becomes 'd' (genealogical abbreviation for daughters).
'thrown in' means one lot of letters goes inside another.
'nettles' becomes 'riles' ('rile' can be a synonym of 'nettle').
'd'+'d'='dd'
'dd' placed within 'riles' is 'RIDDLES'.
(Other definitions for riddles that I've seen before include "Conundrums" , "Funny little teasers" , "Tricky questions" , "problems" , "Puzzles and mysteries" .)