Swain clumsily embraced lover's first family after marriage (2-4)
I believe the answer is:
in-laws
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for in-laws that I've seen before include "A person's relatives by marriage" , "Spouse's relations" , "Relatives by marriage 2-4)" , "Family of your spouse" , "Relations by marriage" .)