The rules should answer your Q's, but I do have one for you--do you really think 15% of every alliance is multies? That seems a tad high...
To help quell any undue paranoia...you don't need to change your procedure and don't have to screen people to see if they're multies for any moderation-related reason. You should report any you do find, though. A lot of alliances complete the scans for internal security reasons but do file multi reports in the Game Abuse forum or send in private reports (to Game Mods), partially because it is in the rules to do so, but also I suspect because of in-game reasons. Like not wanting to have cheaters in your ranks, sure, but also because it stands to reason that you might be busting in-game enemies trying to spy on you (or have their friends spy on you from a shared network) and the like. Whatever the reason, it shouldn't be too time consuming, just send in the report it sounds like you're already compiling.
Do you do this once a week or so? I wonder there's been so many just in the last week. I guess it [i]is[/i] mating season...