Mission 13: Devil’s Dalliance
After the initial waves of enemies are over at the start of the mission and the ramp appears ahead of you, turn around and hop up the ledge behind you. Grapple over to the left side and the key will be on the walkway there.
After you enter the club and fight off the first few waves of enemies, a ramp will appear and you will be able to proceed. Instead, turn around and climb up the ledge behind you. Once up, go to the right and you will be able to grapple over to the door there.
This can be found behind a wall to the right of the divinity statue just after round 5. To reach it, walk to the edge of it and look down to see the door. Drop down to access it.
Mission 14: Last Dance
Mission 15: The Trade
For the first key, hop to the left of the crates when you land on the red jewel just after hoping on the car. Jump down to the ground and the key will be on the far side of the crates there.
Just after you pull the bus out of the way, hop to the left of it and there will be a fenced in area to the upper left. Hop up the crates there to reach it.