Twins have to gain (3)
I believe the answer is:
win
'gain' is the definition.
(synonyms)
'twins have' is the wordplay.
'have' says the answer is hidden in the clue.
'WIN' is hidden in the letters of 'twins'.
'to' acts as a link.
(Other definitions for win that I've seen before include "Trumph" , "Come first" , "Achieve victory" , "Be victorious or succeed" , "Finish in first place" .)