I heard that original owners own DOS II were being upgraded to the Definite Edition at no cost to the owner. How does this work out with the pre-orders. The video says that the kickstarter backers were getting it, however it does not mention the people that joined the community later (buying the game) before the DE came out.
Are the people that have the non-DE version also getting the DE pre-order offerings as well?

It looks like not just the backers but everyone...and especially if we purchased recently. Is there an answer to this?

I haven't seen confirmation stated anywhere. I was hoping that Larian would comment on it here.

Every article i've seen stated that it's a free "update" (basic version will also stay) for every owners of game.

Is the Definity Edition an Upgrade or would I have a two "Divinity Original Sin 2"-games in my GOG library?
In my Steam Account I have two separate Games of the first game.

I thought it was already released, at least on their site it shows as Available for PC. I guess it hasn't been made so on here?

It's expected release date is August of this year.

It will be released at the end of August. It will be an additional item in your library, just like with the original D:OS and its enhanced edition. It's indeed free for anyone that already owns D:OS2, regardless of when they bought it.

Looks like it has been confirmed. Users that own the original DOS II will get the Definitiive pre-order bonus.