I'm so glad you think it's amazing, thank you for saying so!
1. One enemy squad typically deals a single instance of DAMAGE, regardless of how many members there are in the squad—think of individual squad members as almost like "HP"/"health bar stages" of the squad (which sometimes has other mechanical consequences) rather than discrete actors. So basically: you pick an item in their inventory and deal that DAMAGE to the player.
2. If there are multiple enemy squads, I generally pick one that I think is more fun/interesting/narratively logical and apply that squad's DAMAGE.
3. Field rulings always trump all of this! If you think it's more fun/interesting/fair to have all the enemy squads apply DAMAGE, go for it, as long as players feel adequately warned & you have a clear reason for doing so. The new Faithless Edition coming later this year will have more guidance/a new system for "warning" players do that consequences feel fair—if you want to playtest it, feel free to contact me here for a draft copy. I will say: most instances of DAMAGE (not all) are enough to kill a player who isn't using ASSAULT'S NANOMESH or who isn't in a vehicle, so at that point, it becomes more about flavor. If the PC is ASSAULT, in a vehicle, or otherwise stand a chance of surviving a hit, field ruling that multiple enemy squads deal DAMAGE is going to affect balance more, and you should weigh that when making the ruling.