Tapping doesn't change how much damage something would do or whether it does damage at all. Also, Dragon-Style Twins will already be tapped because you tapped it to attack.
And Deflecting Palm will only prevent and deal 3 damage. It applies to the next time a source would deal damage, not each time. Therefore, it will only stop the first strike, or 3 of Dragon-Style Twins's 6 total damage.