1. Master Chief (With an assault rifle, shotgun, and DMR.)
2. The Arbiter (With a covenant carbine and an energy sword.)
3. The Last Dragonborn (With a full set of daedric armor, and full set of dragonbone weapons. All spells and shouts. No potions or enchantments. Gameplay DB, not lore DB.)
5. The Ashen One (With full Armor of the Sun set, Lothric Knight Sword, Longsword, and Black Knight Shield. All spells. No potions.)
Fight takes place on Titan. The team has an hour to prepare and plan their attack. Prep time would be taken away if the fight is too one sided.
Thanos has all infinity stones except the time stone. He gets no prep time.
Basically just take the battle on Titan in Infinity War and replace Iron Man and his team with these guys.