Yeah but numerous stern telling offs haven't worked in the past. And now the Saudis are all pumped up since they started a military confrontation with Yemen. They are in fighting mode and want to take care of all their problems at once.
If the Saudis believe that Qatar's help or at least their less than complete hostile attitude toward Iran is in some way helping the Houthis in Yemen then as part of their plan in Yemen they might well want the Qatari's to quit their independent foreign policy immediately. Therefore, attacking Qatar could well be part of the overall Yemen policy.
If Trump has green lighted this the Americans aren't going to do anything, they'll just sit and watch from their air base.