??
You have blown the whistle after the 1st retaliation, the game is stopped and the original late tackler then wades in and punches the guy who punched him?
Very very very loud whistle - you are about to get a 30 man man brawl, the whistle may stop it happening ..... but probably won's. Get ready to observe who then does what to whom.
When the dust settles red card the original late takler for the secondary retaliation, red card someone from the other team who ran in from a distance and punched an opponent - there will be one - read riot act to captains - restart with the PK against the original retaliation. - be prepared for criticism, many will say you can't ref like that.
Treat such comments with scorn, and show that your actions actually calmed the game down, and let rugby break out - which they will do and which, frankly, is the objective.