We've been seeing an issue crop up today where some players are unable to redeem the additional copies in friend packs. Unfortunately, this is caused by Steam and we can't do much at this point except ask them to fix it, but if you're experiencing this we encourage you to file a support ticket with Steam.
In the meantime, you can head to the forums to request extra beta keys for any friends who are having trouble activating the game: http://gunsoficarus.com/community/forum/discussion/219/beta-key-requests