SureAI

I have a couple questions as a skyrim legendary edition owner:
1. Will the DLC still work with the game, aka can visit solstheim/ fort dawnguard/ castle volkihar/ soul cairn etc or will they be inaccessible?
2. If the DLC don't work will there still be some of the content such as NPCs like Karstaag or Ebony warrior or vampires? What about items e.g Crossbows and Riekling spears or spells, powers and shouts such as dragon taming.

Read http://sureai.net/games/enderal/?lang=en at the bottom.

I think you have a misunderstanding of what Enderal is. When you play Enderal, it is a completely new game, it is not just a modification placed within the world of Skyrim. So you will not see any Skyrim DLCs because you will not see Skyrim.

If you read his question, you can't automatically assume he doesn't get what Enderal is. It's possible his confusion is the way bethesda rpgs technically work. He may be thinking that since the dlc is not required to run Enderal, that the dlc is not overwritten with anything having to do with Enderal. So what happens in the game if you have the dlc? You don't run the esm files associated with the dlcs, if I'm not mistaken. I'm not playing the german version to know, but I would guess that launcher thingy handles that for you.