Working with those people with aim to be getting better (2,3,4)
'be getting better' is the definition.
(I've seen this before)
'working with those people with aim' is the wordplay.
'working' becomes 'on'.
'with' means one lot of letters go next to another.
'those people' becomes 'them' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'aim' becomes 'end' (I've seen this before).
'on'+'them'+'end'='ON THE MEND'
'to' acts as a link.
(Other definitions for on the mend that I've seen before include "Making recovery", "undergoing recovery?", "Regaining health", "Looking up", "Improving in health".)