Out to get the son in, will get rid of (4)
I believe the answer is:
oust
'get rid of' is the definition.
(I've seen this in another clue)
'out to get the son' is the wordplay.
'to get' is an insertion indicator.
'the son' becomes 's' (genealogical abbreviation for son).
'out' going around 's' is 'OUST'.
'in will' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for oust that I've seen before include "Expel (from a place)" , "Show the door to" , "Overthrow" , "Give marching orders" , "Drive out, expel" .)