I completed the Thirsk hall quest in favor of Nords and yet Thirsk hall is always under attack by Rieklings, even after completing the quest. The NPCs seems to be essential so I'm not woried about loosing any of them. I'm rather annoyed by this constant repsawning of the little blue pests every time I go visit the blacksmith there.

I wonder if there's a work-around or something, maybe with the console. The quest ended fine, as far as I can tell.

That's what happens, when you re-take the Hall (for the Nords).
If you do it the other way,

But strangely (inconsistently?) Rieklings still attack you on Solstheim.

They never appear for me in Skyrim or Solstheim, and i completed the quest in favour for the little pests.

It's not a matter of choosing which side; every week or so, the useless little pests wreak havoc again in front of the Thirsk hall even if the quest is ended. Is this intended? If so, why they only gang on the lone smith outside (which is essential, btw).

Yes! If the quest is ended then you chose a side.
If Rieklings are constantly attacking the Smith,
Good thing he is essential, heheh...

Sooner or later
Again, I was hoping to 'make friends' all across the Island... but not.
I guess I'm invading their homes, so...