Alright, here's the battle map.

[img]https://i.imgur.com/UAVZAyK.png[/img]

Remember that Alchemist Fire doesn't have a splash effect, it's a to-hit to light an enemy on fire. The enemies except the big one is surprised, so you'll get advantage against them, but the big one isn't as preoccupied as the rest so he'll get to act normally. Additionally none of the enemy's are within the regular range of an alchemist bomb (20ft), so your advantage from the surprised round negates the disadvantage from the long range throwing. Alternatively you can hold your action until they get closer, but you won't get the surprise round advantage.