Sorry Dungeon Master, it is my assumption that this is a narrow passage within the wall and that Velon is at or near the rear of the party column. Lia instructed Poljen, Mari, Oswald and Zarra to take the lead, although I remember Poljen commenting on standing aside so the silent killers could do their thing. I'm guessing their actions are the key and should take out two guards.
From the rear of the main party can Velon see down the hallway where these two are? I could have him ready Hold Person again on the condition that one escapes the initial attack and starts to flee.
Is Poppo referring to Fay and Jack? We are nowhere near them. It seems like he is getting them mixed up with the scouts for the main group? We have no idea what the two invisible scouts are doing and no control either. It is out of our hands.