Found this easiest to do on The Teague Temptation. This was on the XB1 version, in case there's any variation between platforms.
Start in the AV area with a silenced pistol, a lockpick and coins. Hide your pistol (and later, the letter opener) when not in use.
Immediately run to your right towards Courtland Aupry. Throw a coin near the equipment between you and him, so that the witness near him is the one to investigate. As he's bending down to pick up the coin, you want to push Aupry over the railing. Immediately run back the way you came and through the door, then down the stairs on your right, all the way to the kitchen. Head around to the right and through the exit. Because you won't pass any cameras, this path can be taken for Levels 1 and 2 identically.
Same as before: Immediately run to your right towards Courtland Aupry. Throw a coin near the equipment between you and him, so that the witness near him (closer to you) is the one to investigate. As he's bending down to pick up the coin, you want to push Aupry over the railing.
Now, run back to your starting point, wait for Benoit Lagarde to leave for the bathroom, and shoot the camera ahead of you when he's out of earshot. Run up and to the right, and at the other end of the area is another security camera. Take cover behind the crate and shoot this camera too. Run forward and to the left, and on your right is a door you can unlock. This is the Sheikh's suite, if you're fast enough he might still be out on the balcony. For now, take cover behind the long desk in front of you.
Wait for the Sheikh to walk inside, he'll take a phone call. Then he'll walk back outside onto the balcony. There's a security guard in here, you need to distract him to grab the letter opener on a desk on your right. So work your way up to between the two couches, and shoot the wall at the far end of the room, so the guard looks that way. Quickly run up and grab the letter opener, and exit the way you entered. Run all the way back to where you shot the first camera, and head through the doorway to the bathroom on your left. Here you'll wait for Lagarde.
Make sure your letter opener is hidden when he walks in, then sneak up behind him, equip the letter opener, and silently kill him. No need to hide the body, just start heading down to the same kitchen exit as before. Because you're not pacifying anyone else, and not changing disguises, this will work the same for the final three levels.