how to beat all 3 egiption god cards at once

Well, this can be quite simple if toi think about it.

If all your opponents monsters are face up, use lightning vortex which will destroy them all at the cost of discarding one card. toi might want a trap ou magic jammer to help this in case your opponent has a counter.

toi can also use man eater bug with Book of moon (x2) ou book of eclipse.

Before the monsters are a threat though, toi can also set Solemn Judgement, with the cost of halving your lifepoints to negate the summon of a monster.

Deck the guy out. Use the Iron Chain cards. Use cards that help increase your own Lifepoints, so, that way, he/she will never get your Lifepoints down to zero.

How about watching the final duel part 2 and there's your answer

Use the trap card pyramid of light it will automaticlly destroy all three gods if on the field and banish them out of the game.