This loadout took me nearly an hour.
All consumables are to be saved for the final battle.

2x Psykers with Solace and Stasis. One with Domination. <- ESSENTIAL for counter Avatar tactics, they negate mind control and freeze the enemy. They also carry non-essential but nice-to-have gear.

Gunner with AP rounds, Chainshot ability and a deployable Senry Gun. <- Main big damage dealer, but slow. Relies on Avatar teleporting near then chain gunning.

Assault with Wraith Suit, Dragon Rounds, Close Encounters <- 2nd damage dealer, hunter-killer unit to flush Avatar out of corners.

Infantry with Bluescreen rounds & lethal perk - Support unit to keep Codex numbers in check. (Codex's WILL strangle kill your team to death in the final, ammo is life).

Grenadier with Acid, perk flashbangs and the Plasmabow - Flexable support unit, Acid to strip Avatar protection, then accurate hard hits and misdirection.