Going to be trying T7 soon probably and just a few questions:
1. Is it cursed voice that you should make sure you are facing the Renauds for? (to petrify them)?
Voice, yes, if you're the healer with voice (and if you're healing, turn auto-face-target off, you don't want to turn to voice the Renaud then heal MT and oops stone everyone) Everyone else faces the edge of the arena, away from everyone.
2. The vids I've seen, people don't kill the Renauds right? Why is that/do they stay up for the entire fight?
Voice is the triangle debuff and means, when the counter reaches zero, you're shooting a conal AOE ahead of you that stones anyone caught in it. Shriek is a circular debuff that, when the timer hits zero, shoots a circular AOE out from you that stones anyone caught in it. The only way to prevent the party from turning to rocks is to have a stoned Renaud for the shriek person to hide behind. The stoned Renaud then LoS's the shriek and prevents stoning the party/buffing Melusine.
Some people swear by one Renaud at a time, some 4 stack, but the idea is that you always want at least one frozen Renaud up for shriek.
Besides that, the fight seems relatively simple anyway.
It's mostly situational awareness; now that the party can eat a shriek and still survive it's pretty easy as long as people keep track of their voices and the OT can grab and hold the adds. Venomous tail, petrifaction, voice, shriek. It's mostly just knowing what's going on at any given time that's key. Getting 8 people to all pay attention can be tricky though.