@duskshine749Looks like Prince Alexus and CollectorofMyst have your back, so I'll just re-iterate :D
Your best bet is to take one step forward and shoot, as you get bonuses with pistols. Taking a step forward means you can make a ranged attack if the hellbats beside you aren't dead.
You can also tell me what you would like to prioritise. So for example: I want to shoot to kill as many hellbats as possible on my turn. If I have any shots left over, hit the Tentacles as well.
Or:
I want to shoot all my shots at Tentacle # to try and kill it. Or I want to spray all my shots to hit/deal damage to as many tentacles as possible.
You can do melee instead if you have to, if you prefer, but I wouldn't advise it since you have pistol bonuses. If you can't make a ranged attack for whatever reason, I will assume you'd rather do melee so you can still do damage though.