This shows very poor door-opening practices on the part of the party, and extremely poor defensive positioning on the part of the orcs and orogs.
Its a party of a Wizard, Ranger, Cleric and Rogue in formation in a 10' wide hallway, opening a dungeon door and fighting Orcs in the room beyond.
I almost couldn't get more 'standard party in dungeon doing standard dungeon stuff' if I tried.
Assuming that the time pressure precludes standard door procedures (e.g. rogue sneaking up and listening, then reporting back with intel to formulate a proper breaching plan) the safest way to open that door blind is to have the Bladesinger precast Blur, then open the door while the rest of the party is in full cover at the top of the staircase you described.
You now have an isolated Wizard with a spell pre-cast (with a 1 minute duration) and the rest of the party 50' behind and up a staircase and unable to even see into the room, let alone support the Wizard. The Cleric with his 25' move needs to dash just to get down there, and as long as the Orogs stay back other PCs cant even see them.
If the room had some kind of AoE monster in it, or Save or suck monster in it, the party are a round away from helping the wizard. Also, the Wizard would want to pray there is nothing in the room with blindsight (ignores blur) and also that he wins initiative vs the rooms occupants.
In this case you know its Orcs sitting around playing cards (or whatever} in the middle of the room.
Thanks to your tactics, a few might now run off and alert the rest of the dungeon for reinforcements, and there is little the Wizard can do about it.
Instead, the Orcs need to be put down fast and decisively.
Given the moronic enemy guard formation, you are correct that Fireball is the optimal plan: with the time pressure killing the enemies quickly
Its not just time pressure that is paramount (and they have 4 hours, so they actually have time for a Short rest or two), its resource management.
Fireball likely gets the job done with the least party resource drain, preserving slots and hit points for the 5-5 encounters to come.
Dashing through the room cost the PCs a 3rd level slot from the Cleric, 39 HP from the Rogue, a use of Bladesong, and a shield spell (to date). Unless the Bladesinger can stop the Orc from executing the (failed one death save already) Rogue before the Orcs have a turn (they go next), its also going to cost them a diamond and ANOTHER 3rd level slot on the Revivify for the Rogue (plus some HD and potions or more slots to heal the Rogue) plus the Orogs (who go first) might also drop the Spirit guardians (as they're likely to now attack the Cleric).