That is creative. But also unnecessary. I had a typo. The door is not locked.

"Thank goodness. I was worried you were more of those thugs having realised your mistake. I am Renaer Neverember. I was concerned that Floon was too intoxicated to find his way home by himself and offered to escort him but we were jumped by five thugs as we left Fillet Lane and taken here. And then more thugs broke in, killed the original five and took off with Floon. But only because I managed to hide in the commotion, and Floon was bound tighter so couldn't get free and I think they thought that he was me. They have no reason to take Floon which is how I know you are not one of them"

Xaul takes in this information, and thinks it through thoroughly, trying to pick out any lies. Insight: 14. If he detects no deceit, he'll say 'Okay then, we heard from the kenku through the other room that they took him down the sewers. Can you guide us to where they went so we can go after them? We've been instructed by a man named Volothamp to find him, I'm sure you'll know him too.' If he detects any dishonesty, he'll call the rest of the party in to up the interrogation. 

Just before she can wrench the door out its fixings, she grips the door handle to help the crowbar under the newly exposed door setting. With a click it opens.

Ah, she thinks, I turned it the wrong way. These things happened, but to her more than most others, it seemed. 

She enters the room to look for clues.

No dishonesty detected, but you do detect that he is feeling guilty. 

"I am afraid I don't know where they went. The left the building to get to the sewers. And as a noble I do not find myself entering the sewers on a regular occasion. But for Floon's sake I will happily accompany you." and (assuming that you let him) he will go and grab a rapier and dagger from the bodies of the fallen enemies.

Skye there are no clues, the rooms all seem empty. There is one thing you find of note. A box with a single piece of paper and some instructions. It is a paper bird

Xaul lets him gather up some weapons, and then introduces Renaer to the party. 'He'll be our guest of honour on our trips to the sewers, but it looks like he can swing a sword, so maybe he'll be of some help.' He then knocks on the door to the room Skye's in and says 'Any clues in there? We've found Floon's drinking buddy, and he'll be heading with us to the sewers to chase after him and those thugs, so if you've found nothing in there, best we head down there through a manhole or the likes.'

Quote from Swiftgale >>

No dishonesty detected, but you do detect that he is feeling guilty. 

"I am afraid I don't know where they went. The left the building to get to the sewers. And as a noble I do not find myself entering the sewers on a regular occasion. But for Floon's sake I will happily accompany you." and (assuming that you let him) he will go and grab a rapier and dagger from the bodies of the fallen enemies.

Skye there are no clues, the rooms all seem empty. There is one thing you find of note. A box with a single piece of paper and some instructions. It is a paper bird

 ((Does she know what a Paper Bird is from her background/ has it been used — are the instructions in the box or have they been delivered on the paper bird. 

Either way, what do the instructions say when she reads them?)) 

The instructions are on the box. As in, instructions of how to use the paper bird.

While you are discussing what to do, a dozen of the city watch burst through the doors. "Everyone down!" and they quickly take the two surviving kenku into custody, and go to take the lot of you as well, quickly determining the Xanths and Zhents. "Stop. They rescued me. Captain Staget I believe? You should recognise me." "Neverember. Okay. Just this once I am willing to overlook any crimes you may have committed here, though I don't believe these bodies are all from you. No way those groups would work together. Just for reference though, I do need to give you this" and he hands you a copy of the code legal.

Xaul is taken aback by the sudden raid, but it seems Renaer has it under control. He approaches the watchmen and says 'Excuse me, gentlemen, we are a party of Warlock adventurers that have been hired by Volothamp Geddarm to track down his friend Floon. Over the course of our investigation we have uncovered more of the truth, and have came to develop the understanding that both Floon and Renaer here were caught in the crossfire of a gang war between the Xanths and Zhents. Renaer managed to escape, but Floon was taken by members of the Xanathar's cult into the sewers, and we intend to make chase after them to retrieve our employers dear friend. Please, would it be possible that you could provide us with any help, such as men, weapons, or items of magical potential, or at least provide us with some legal coverage so we are not incriminated for any accidental misdoings we may do whilst we carry out our noble acts?' He ends his long speech and waits for a response, hoping he sold the story well enough to earn the party some support. Persuasion: 16

If Skye is undisturbed in the back-offices. She stays hidden in the backroom behind the boxes while she listens to the raid. She places the paper bird in her back pocket, waiting for any clue as to whether it is safe and wise to come out or to wait till it is all over. 

"I will not be sending any men to rescue someone who might very well be a Zhent or Xanathar Guild spy. In terms of legal coverage, just keep the blood off the streets, okay?"

Damros adds his two nibs, "Might we have your name so if any other city patrols come upon us in our 'sewer survey', we can direct them to you?  Or might we gain a writ of passage, so to speak, for permission to 'Run Rats' in the sewer legally (in the eyes of the city)?"

Damros sighs and ask the one question that he knows will be met with some scorn, "Are kidnappers 'citizens'?  If we end up coming to blows with those who kidnapped Floon -- be they Zhent or Xanathar - will we be prosecuted for 'assaulting a citizen?'"

"You almost certainly won't run into any patrols in the sewers. We avoid them as much as we can. And as for if they are citizens, that depends on where they call home. But as I said earlier, keep the blood of the streets and we won't have problems."

The guards then walk away and you can't help but notice he didn't give his name. But Renaer also noticed and adds quietly "That captain is Hyustus Staget. Very respected by most people in the dock ward. From what I know of him, I think he is glad for the help but he can't be open about it or his superiors will be upset."

Damros slaps his thighs as he looks around the room at his companions.   "That is it then.  We go down into the sewers to rescue Floon.  And keep all chaos and carnage 'under ground' so WE do not end up in the stocks."

If the conversation quiets, Skye exits from the backroom and makes her way to the group. She quickly asks for a catch up from the others. 

Xaul explains the situation to Skye, then says to the rest of the party, and Ranaer 'If we're all clear on what we need to do to avoid being arrested, then I say it's time to head down into the sewers'

Sehaethas says, "I think it's time for us to go our separate ways."

But then, with Kylaski's voice he says, "We're going."

Sehaethas raises a hand to his forehead as he says, "I guess I'll be joining you in the sewers after all."

"Don't worry, Sehaethas (and Kylaski), we will work to keep you alive... and it should be 'interesting' for both of you," Damros smirks as he goes about checking all his equipment and clothing.

Someone give me either a survival or (I assume this one) a persuasion check (with advantage from helping) to find or get directions to the nearest sewer entrance

[No joke I rolled two Nat 1s in Persuasion for a total of 3. Ignore the wisdom save in the log, that was a misclick]