what do you do with the elder scrolls once you completed dawngaurd as a vampire

Dexion's dialogue doesn't trigger, because of a bug when siding with the vampires.
Typically, you should be able to sell them to him, but currently it is only if you side with the Dawnguard.

Please use the search next time as this has been answered many times.

The Blood and Sun ones to Dexion. The Dragon one to the Orc in the Arcanaeum, College of Winterhold.

Not if you already sold it to him and had to buy it back for the DLC; at least that is how it was after I beat the vampire plotline.

I read about that. It's kind of disappointing devs didn't find a solution for that instead of leaving players with 20 points of weight. I also genuinely hate the fact we are forced to kind of join the College to simply bring an item to a guy. I mean, hey Faralda, why don't you open the damn gates before I Fus Ro Dah you down the bridge? I don't want to become an apprentice... *facepalm*

They don't weigh anything with them being marked as quest items, all they do is take up space in the inventory list.

But still I don't want to have it in my inventory. You know, I like to keep it clean. But maaaybe devs force us to keep at least one Elder Scroll for a next future DLC? It seems they never lose a purpose to be used. Yes, the series is called The Elder Scrolls, but I can't believe every single DLC will have one involved. It would be lack of imagination really.