You need to open by dispeling the taunt with Ezra (or Chopper). Then Zeb and Sabine need to get stagger onto the Death Troopers so their special buff goes away, otherwise they'll tear you apart. From there, kill the Death Troopers, then the Commanders, then the Stormtrooper, then finally Thrawn.
Ezra and Sabine's job is doing damage to whatever you're trying to kill - but the others' job is making sure the team survives. Hera and Zeb should work together to stun Thrawn whenever Hera's not putting Backup Plan on someone (remember Zeb can stun off of Expose if Hera lands it, so they can do this even when she doesn't have her assist call handy), as he's the biggest threat but can't be killed quickly, so controlling him makes a big difference. Kanan should taunt ASAP, remember to use Kanan and Zeb's protection up when someone needs a little durability boost. Above all, Zeb needs to live. If he dies, you lose a big chunk of protection on everyone from his unique, and you no longer get his protection regen. You won't last long without that.
Speaking of, if you haven't yet, omegaing Kanan and Zeb's uniques helps a lot. Kanan's means more counter attacks and more healing when you're hit with debuffs, and Zeb's is a significant durability boost.