If I have more than one Machamp in play, do I get +20 damage for each one of them?
Yes, but only for each one that has the "Fighting Fury" Ability.
Fighting Fury




x2Fighting Fury
Each of your
Pokémon's attacks do 20 more damage to your opponent's Active Pokémon (before applying Weakness and Resistance).


Machamp CrushDuring your opponent's next turn, any damage done by attacks from the Defending Pokémon is reduced by 40 (before applying Weakness and Resistance).
If I have more than one Machamp in play, do I get +20 damage for each one of them?
Yes, but only for each one that has the "Fighting Fury" Ability.