Given that Discover is a movement skill, I assume I can use Discover as a short skill targeting Camo token A and Discover as a second short skill targeting Camo token B. Can I declare a Discover/Discover against an Impersonation -1 marker? Obviously if I fail the first roll the second is wasted (as a trooper that fails a WIP Roll to Discover cannot attempt to Discover the same trooper again). But if I pass the first roll can I make the second roll against the now Impersonation-2 marker? My argument against is the concept of "All at Once" My argument for is Discover, BS attack works.
Which actually raises a question: Can a group activation declare Discover vs the same target? IE an Uberfalls moves within LOF of an enemy Camo Marker and declares Discover. Do you get to make 4 Discover rolls?
Sure, but they're independent rolls. It resolves exactly the same as if the camo marker walked in front of the squad and all 4 models declared Discover as an ARO.
Implicitly you're reading it as "can't be used twice by the same Trooper" not "can't be used multiple times by multiple Troopers". I think that's the intent, but "can't be used twice" isn't that limited.
For me, this comes down to the fact that pretty much only Discover and Baggage contain language about how many times they can be done per order. Baggage describes an entire Order Skill and then says "This effect may only be applied to one Allied Trooper per Order." The only time that limitation is going to come up is in coordinated orders, Peripheral and the like multiple trooper order situations. But Discover says "This Skill cannot be used against the same Target twice in the same Order." In a similar manner, the text for Short Skills says: Short Skills: Can only be combined within the same Order with a Short Movement Skill. Cannot be declared twice or be combined with other Short Skills. Since the conclusion that you can't use Short Skills in a Coordinated Order (because that would be declaring them twice) is garbage, the conclusion that you can't declare Discover in a Coordinated Order (or a Peripheral situation) is the same.