Sue assumes two fellows in charge to be enough (7)
I believe the answer is:
Here is my best explanation:
'be enough' is the definition.
'sue assumes two fellows in charge' is the subsidiary indication.
'assumes' indicates putting letters inside.
'two fellows' becomes 'ff'.
'in charge' becomes 'ic'.
'sue' going around 'ffic' is 'suffice'.
'to' is the link.
(Other definitions for suffice that I've seen before include "Do", "Be enough", "Be adequate" and "Serve - do".)