My team was Shulk, Dunban, Sharla.
Bascially, you want to Topple Xord. But he resists Break and Topple, so getting a random Topple on him won't happen. What you need is a Chain Attack. So try to ignore Xord, run away from him, get him to hit Dunban, just make him a non-issue as much as you can for the beginning of the fight. He can get stuck for a while if you use the terrain as an advantage.
Now you want to pull off effects on the other opponents. Side attacks, Back attacks, anything that raises the Party Gauge. Remember to hit those Burst Affinity QTEs, too. Don't die, if Xorn starts targeting someone at mid HP, toss a Monado Speed that way to buy time. All you want to focus on is three bars in the Party Gauge.
When you get it, unleash! Use one of Shulk's Break Arts (if you're to his side, use Air Slash) and Dunban's Topple Art. Then hold down Zr and press up to have the party focus on your target. If you've got a Monado Buster charged, now's the time. Get him to half HP and the fight ends.