This can be achieved on Mission 9 Hometown. Once you pick up the gun off the table i would suggest moving back like i did. There are multiple ways to do this but i found other ways to be a hassle. You can call and move as many times as you need to. Where ever your brother is when you call will be where you are trying to direct them so you will have to play off of him and where he goes. Line both soldiers up get close and as long as you aim chest level you should get this to work. If it doesnt work you can keep reloading the checkpoint.