No need to go all the way down to the helicopter area. Go out like you’re going to go to the Armory Roof (where Block is), halfway down the stairs, and then climb down the pipe to get to the ledge past the windows.
For the second target, I found the easiest angle for the Sieker was to shoot from the ledge outside the window. Emetic briefcase can also work well, as there’s a briefcase you can use nearby.
With the Sieker to get the first target, I found no need to ness with disabling the cameras either. I saw none on the way to the Keep rooftop exit that needs the flare, or the one on the way to the Arc Winch exit isn’t hard to dodge.