
They are all in the same squad (for the match, doesn’t have to be the same “Squadron”), if they are close enough to each other, each of them will get a “Teamwork” award when one player in that squad gets a kill.
So, if all 4 of them are near each other, then 3 of them will get the Teamwork award.

So, the “Best Squad” award is based on the total number of “Teamwork” awards for the match that the squad was awarded. The squad with the most “Teamwork” awards then gets the “Best Squad” award at the end of the match. That is what the “Awards: 66” is tracking in your screenshot:

66 awards / 3 Teamwork awards per teammate kill = ~16.5 kills total for that squad.
They needed at least 16-17 kills total for their squad to reach 66 total Teamwork awards. That is ~4-5 kills per squad member, on average. It is easy to get that many kills in a short period of time for a skilled squad.