As your starting point, pick the Northern landing zone. Right after you have landed, as quickly as possible, head out for outpost 20 (i.e. to the South-East). Because reaching the point quickly will make it easier, for you, to rescue the engineers. Along your path, you come across outpost 16, which you'd better walk around on the left. Then, walk through the valley and head towards outpost 20, along a straight line.
Slow down a bit, after you come close to your destination, because the area around outpost 20 is being patrolled by, at least, two soldiers. Use binoculars to do reconnaissance/ The engineers are being kept in the green tent shown in the above screenshot and you can use the help of D-Dog to locate them.