Tann said that the Imp disappeared (became invisible) when Nomad attacked it so no one could see it, then SilentOne said that the imp was standing between the two big rats again...after Tann had said the imp had disappeared.
These combat sequences happen quickly. Each character is reacting pretty much at the same time as it is their "point of view". We don't have to wait for other to post to determine our action but we can. As for the sequence that thing really happen well that is where Tann comes in. He will roll intuitive for all characters and enemies then roll how the posted action worked. Read what Tann post and work off of that. In the last round you can figure Intuitive from his post, The rats acted first by swarming the guards, Cor acted next with the snakes, Arandur was next by trying to talk to the rats which didn't work. Rayden was next and shouted the warning of the big rats. Lothor was next hearing the warning shot the middle big rat, made a good hit and exposed it as an Imp. Last to act are the big rats. The one Lothor hit which then vanished and the other two two moving apart . So to me that is your combat sequence.
Now if the Bear is written to attack then Tann will role intuitive for it and insert it in the order.
Also the action of a character can negate your action. Say two characters attack the same enemy, if the first one killed it then the second one's action had no effect. It is all chance and the roll of the dice.
Also if the enemy has first inituitive it could change things, say it vanished then niether attacker stand a good chance of hitting it.
It just turned invisible and didn't move then shots into the space where it was last seem might hit, again it is all in the rolls.
so post what you feel your character would do and hope for a good roll.
Pretty much each week we read the DMs post and then we post our intended actions in response. Just because we want to do something doesn't mean it will happen.
A post like: "I shoot the left rat in the heart and kill it" is a bad post as you cannot be sure you will hit, cannot be sure the left rat will still be there based on its actions and other party members actions and you might miss.
"i take aim at the left rat hoping to end its life with an arrow to its heart" is a good post. You say what you want to do.
Then at the DM rolls and figures out the results of combat and makes his next post. That is when you see if what you wanted to do happens.