A1: Walk to the north-eastern part of the map, and climb the fence where it’s covered by gauze. To do this, push the stick in the direction it tells you and then spin it upward. This will alternate before you need to just push it forward at the top.
After that, walk straight ahead being sure not to be seen. You’ll need to move along the fence ahead, moving towards the left until you find a gap in the fence. Crawl through this gap.
From here on it gets a bit harder. Move right behind the blockage and move forward behind another lot of crates. Wait here until a truck passes by and then walk up to the side of it. Hanger 4b is straight ahead of you with a guard standing next to it and another guard stood by the hanger to the right. When you see the truck here, move up to it and wait close until it passes, leaving you in between the two hangers. When it passes, go straight forward into the gap between the hangers. You won't be seen if you do this correctly. Enter the hangar on the left through the gap at the end of the walkway.
Inside, you will tell Markus leave and that you’ll look for the rest. It is possible to get all the boys out in time but it isn’t easy and depends on whether or not you got the mini-game right. There’s one lad upstairs at the end of the platform (the stairs are near the front of the hanger), one in the plane near these stairs and one at the back of the hanger in a crate. Even if you don’t save them all, at least you’ll have saved your brother.