Hi,
I was able to run the objective successfully just yesterday (October 5 2020). Albeit, it took me several retries. I do not know what script is behind the objective, but from my attempts, it looked liked it's just a matter of killing both soldiers at the same time. After some tries, my men finally managed to hit them simultaneously.
BTW, I strongly suggest playing the Scouting mission beforehand and getting the necessary equipment (scopes).