See two sons coming to harm (4)
I believe the answer is:
loss
'harm' is the definition.
(thesaurus)
'see two sons coming to' is the wordplay.
'two sons' means two replacements for 'sons'.
'see' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'sons' becomes 's'.
'sons' becomes 's'.
'coming to' means one lot of letters go next to another.
'lo'+'s'+'s'='LOSS'
(Other definitions for loss that I've seen before include "Defeat - deprivation" , "Cost" , "Deprivation; failure" , "Destruction" , "(Sports) defeat" .)