Thx for all the replays, we managed to beat it for both our wars using the WHMx3 > BLMx3 method.
After trying many many times with different setups this is byfar the best one or at least the less suscettible to random facts like spawning aggro or spawning point.
To make sure each wave was shotted by the Holys and Firaga we had each one use a Mega INT pot at turns one for each wave

1° pop: WAR runs full buffed and use Mighty Strike > Overpower (keep TP for second) and WHM do Holy x3
2° pop: WAR SC asap and WHM do another Holy x3 then switch immediatly to BLM and run out
3° pop: run far away and rest full MP, then go near and Excurciate > Resonance > Firaga (3 crit firaga are enough to 1shot them all)
Then do first boss with the BLMs from outside and change to DD setup for last boss, full party buff is nice here since last boss seems quite evasive without.