Yeah, this wouldn't work (or be legal in regards to the EULA) the way it seems to be getting described if you're buying multiple copies for folks on your TGN account.
If you're getting this for a LAN of PCs that you own, then first thing is that 1 Sins serial is good for 2 PCs.
If you're buying another license to play on 4 LAN PCs, then that's fine. You'll need to put your email address in the Stardock Support email form (https://www.stardock.com/support) and it'll send you an email with all your serial info. You'll need to register the game manually on the other two PCs since SDC can't deal with that itself, however.
1Spartan - You should email [email protected] about that stuff.