As tank, what should I need to do, tackle the beast itself or operate the cannons that are there? Or are the cannons the dps role in that battle?

My initial attempt ended in a mess, as I tried to tank under Vishap, the big one itself, and the adds were right in the way, as the others tried to take them down. In the end, we were wiped.

Just so you know, the party were mainly newbies.