I am some-what confident on what you were trying to do, the idea is really great! It just requires a bit of polish, You could have made the 1,2,3,4 for selecting the characters, I can see the code is well made the pathfind of the enemies and your characters goes accordingly. It just requires some small improvements here and there like: having a bullet trace when they are shooting. Randomized positions of the extraction points, It doens't need to be 100% random you could put already defined extraction points and have code choose what predefined position of a list. It should probably tell you where the extraction point is, with an arrow pointing at it. When the press the button to throw grenades you should code the throw where they are already shooting.
But overall nice game!, I had my fun with the game.