Comedian taken in by old Americans working together (2,7)
I believe the answer is:
in cahoots
'working together' is the definition.
'comedian taken in by old americans' is the wordplay.
'comedian' becomes 'hoot' (both can mean a funny person).
'taken in by' means one lot of letters goes inside another.
'old americans' becomes 'incas' (historical South American civilisation).
'hoot' put into 'incas' is 'IN CAHOOTS'.
(Other definitions for in cahoots that I've seen before include "Working with" , "Associated with" , "Conniving" , "Conspiring together" , "what conspirators are" .)