This scenario always causes a discussion at our table...probably because I'm not good at handling it,
I thought you could only ready partial actions... Thus nobody readying an action gets to do a hell of a lot more than the one bashing the door down...
And only readied actions happen just before the occurance that triggers them... Thus readying an action to attack when the door is open, not when he opens the door...
Delayed actions happen after the action has occured. Thos those that delayed, can only act after the door opener has completed his entire actions for the round. You can't interrupt an action by delaying... If you delay, you wait and see what happens, THEN act, after the fact.
SO depending on who delayed and who readied what for which trigger, a whole lot of different things can happen.
Ties are broken first by Dexterity score, or at least so rule we. So most orcs or gnolls, will not be acting before at least the rogue or dex fighter/archer that readied an action. Most likely the wizard, if dextrous, will also get off a fireball before the orcs get to chuck their javelins.