Arden quietly moves a bit from his starting position and takes a shot with his longbow out of the fog towards the sound of the crossbow cranking:

Attack: 24 Damage: 8

Damage reroll (Piercer feat): 10

(No disadvantage from not being able to see (feral senses), position is not revealed (skulker feat))

So assuming 24 hits, that's 10 piercing damage and Ronin's turn.

• When you are hidden from a creature and miss it with a ranged weapon attack, making the attack doesn't reveal your position.

You didn't miss, so your attack does reveal your position.

Reaction Attack   Attack: 20 Damage: 9

Ronin takes a deep breath and calls upon his fighting spirit, and his hands move with preternatural quickness as he cranks and shoots repeatedly.

(Fighting spirit to cancel the disadvantage.  +15 Temp HP.  Will use  Sharpshooter for +10 damage and ACtion Surge)

Attack: 28 Damage: Unable to parse dice roll.

Attack: 10 Damage: 16

Attack: 14 Damage: 17

Attack: 12 Damage: 22

Attack: 13 Damage: 21

Attack: 11 Damage: 21

Attack: 19 Damage: 24

Attack: 9 Damage: 19

(BTW  - A ranger?  Why not two attacks and hunters mark or something?)

Note con saves needed for fog cloud I think...