Je joue 2 Stonehorn Dignitary. L'adversaire n'attaquera pas ses 2 prochains tours, non ?

C'est exact. Le lien gatherer indiquait d'ailleurs ce ruling :

9/22/2011 If more than one Stonehorn Dignitary enters the battlefield during the same turn, and you target the same opponent with each ability, that opponent will skip that many combat phases (over multiple turns if necessary).

Thx