Finally register wrong family (4,2)
I believe the answer is:
sink in
'finally register' is the definition.
'sink in' can be an answer for 'register' (I've seen this in another clue). I am not certain of the 'finally' bit.
'wrong family' is the wordplay.
'wrong' becomes 'sin' (wrong can mean a sin or crime).
'family' becomes 'kin' (synonyms).
'sin'+'kin'='SINK IN'
Can you help me to learn more?
(Other definitions for sink in that I've seen before include "Become fully understood or realised" , "Penetrate, become understood" , "Be absorbed" , "Get through" , "Permeate" .)