As others said, Make sure you are STACKED and not close to each other. As a
prot Pally I am able to use Divine hymn every Feud and the Dps who can (ele sham in our case) also throws down Rain.
Feud wasn't our biggest problem actually :P It was when the boss had double attack ready before doing a massacre.
Queue Double attack ->Massacre -> Feud -> Massacre -> Double attack
I was the Offtank and since im a Pally I could alternate Cooldowns with the priest to survive the double attack (with LOH or AD for my part). It's kinda hard on mana to Top a tank in 2 seconds