when creating giveaway of a pack (game + DLCs, multiple games on one key or whatever else) It's up to giveaway's creator how many items from the pack may the participants have while entering. It's all in the FAQs
Also, the "if you can enter..." thing is extremly wrong. Often (especially when it comes to DLCs) people can enter the giveaway even if they own whatever is beeing given, so it's good to check your winners.
Last but not least: when you reply to someone use the tiny grey button labeled "Reply" that you can find under every message. This way people will be notified about the reply. If you don't they have no way of telling wheter they've been ignored or not (also it'll create a fancy layered comment like this one to help with reading! :D)
Welcome to steamgifts and enjoy your stay! :)

Often (especially when it comes to DLCs) people can enter the giveaway even if they own whatever is beeing given, so it's good to check your winners.

FYI, it is the case here: I own both the game and DLC and yet that GA showed up in my list