Easier than it sounds. There's a few setting to change to make it easier to do.
And No, you don't have to do a 5 vs 1 game
It can be a free for all as far as teams go, assign 1 team to each army.
1. Play the Eliminate HQ mode, destroying their HQ eliminates that army amd all their units.
2. Increase how much money per node you can get, increasing the chance of chests could you you extra dosh too, or lose units.
3. Set every army, including your own to Guardians. They have little to no air defense except any air units they have.
4. Build a swarm.or air units, get at least 30 for safety.
5. DO NOT ATTACK ANYTHING until your ready to wipe them. Then just swarm a base and hit the HQ, you will lose a few units, but nothing you can't replace.
6. Build more drones to do the next 4 attacks, until you win.