I have the same question. I own the base game and none of the DLC.
@rustypani: thank you for the giveaway and welcome to steamgifts! In the case of a package like this, a base game and DLCs in one key, there is no technical way of the platform to specify which kinds of entries should be allowed, but you as the giveaway creator can tell people what you want to allow, and at the end you should check your winners.

Steamgifts cannot determine if an account owns DLC or not, so it's possible for someone who already owns all parts of this Definitive Edition to enter this giveaway. This is why you should check the winner's steam account.

sure

Can we enter for the dlc if we have the base game?

Yes, that happens for some bundles when the site can't detect that you have the bundle.