I have exactly the same issue with a Family Feud quest in Zestea (or somewhere round there).
Find naughty guy who's in hiding, take him to leader chappy in other village, try the various persuasion options (74% & 59% as per OP, so I thought I was looking good), he doesn't go for it, fight starts, naughty murdering chappy gets killed, failed quest.
Another time I went straight for the fight with my companion in tow. Not really what happened, but all of a sudden we were in normal comms mode with the previously angry leader type, no idea what happened to naughty murderous bloke, and quest is still open with no apparent way to re-engage with the angry leader.
This is my first few hours with WB btw, so I'm a complete newb