Emerald WEAPON:
Party - Cloud, Tifa, Yuffie
Equipment - preferably ultimate weapons and Mystiles / Imperial Guards
Essential Materia - Master Command=HP Absorb, Double Cut

Quite a simple method really. Each times a character attacks they do so four times, absorbing HP each attack, so you shouldn't run out of HP in a hurry. Use Limit Breaks when they become available, and if possible, Mime them. As you only have 3 bits of materia equiped Emerald's Aire Tam Storm will only hurt 3,333. Use Pheonix Downs to revive a character as soon as they go down.

Ruby WEAPON:
Party - Cloud, Tifa, Yuffie
Equipement - as above
Essential Materia - Revive=All, Double Cut, Hades

Make sure Tifa and Yuffie are KO'd BEFORE the battle begins. On Cloud's first go have him cast Life2 on them both. Making sure they're dead before the battle stops Ruby from doing the Whirlsand attack. Cast Hades on Ruby. This makes him Stop, as well as making him vunerable to physical attacks. All you need to do now is keep attacking him and casting Hades whenever the effect wears off.