Tock's shot catches the hobgoblin in the middle by surprise, the arrow hitting his shoulder solidly. The goblinoid guard screams and curses, perhaps noticing he made a mistake and, unlike his fellows, he gave away his cover too much to take the shot.
Aeiyan barely has the time to reposition himself near the location of the dancing lights, but has the feeling he managed to remain unseen under the dense foliage, thanks to his knowledge of the woods. [No time for an attack during the surprise round, tho]
The first regular round of battle starts now, and this will be the initiative order:
Bartleby 19
Sulannus 19
Hobgoblins 13
Aeiyan 10
Rejik 9
Tock 7
Bartleby and
Sulannus are actually free to decide which one goes first although it probably won't change much (Sulannus however can still choose if targetting the wounded hobgoblin or another).
There are now one wounded hobgoblin standing visibly on the middle boulder ("middle hobgoblin") with no significant cover, and the other two ("left hobgoblin", "right hobgoblin") are to the sides of the cave entrance and have some limited cover to shoot from behind.
Aeiyan ,
Rejik and
Tock can wait to see what the hobgoblins do and re-declare their actions then.
All of you except
Tock (who has revealed his position) are still hidden, therefore have advantage on attack rolls against the hobgoblins (
Sulannus can roll again to check for a critical!).
[sblock=Behind the curtains]Took me a while to decide how to handle this slightly unsynchronized situation

because the hobgoblins had attacked outside the regular initiative roundabout.
I ruled that
Tock's shot had to be quick to catch the hobgoblins by surprise before all of them could get back to cover, but then it also caught everyone else surprised, except
Aeiyan who was on its way already.
An oddities I had to sort out also... I couldn't easily found what happens in case of a tie in a skill contest, which was the case of
Aeiyan's Stealth check. Now I've found that the (new for me) 5e resolution method is "the previous situation persists", i.e. he remains hidden.[/sblock]