[Possible Spoilers] Multiple of the same "follower" bug

[DeltaWulf]

So, I got the summon Durnehviir shout during the Dawnguard questline, did all the stuff with summoning him and learned the new shout from him, etc, etc. A good 8 or 9 hours later on, I've been working on questing and doing the Dark Brotherhood line in specific. I was going to deal with a mark, the Alain Dufont contract for Muiri, and summonded Durnehviir outside of the Dwemer ruin to deal with some bandits and trolls. After returning from inside the ruin, Durnehviir was still there. I fast traveled to Whiterun for something and noticed, strangely, Durnehviir hadn't despawned yet and was actually flying around inside of the Whiterun town cell.

Now I've got a permanent Durnehviir following me, and, in an attempt to get him to despawn, I waited for an hour and ANOTHER Durnehviir spawned in. I tried again, and another appeared. So, apparently, every time I wait an hour, I'll have another one spawn. Having an unlimited army of undead death dragons at your disposal is kind of hilariously supervillian-class material, but at this point in the game I just want him to go away.

Is there any way to get him to finally despawn? Will I have to kill him with the console? Maybe even just disable all of them that have appeared? I don't want to do anything to permanently "delete" him from the game, but I don't think the disable command will do that considering it seems the shout spawns a unique Durnehviir every time you use it.

Also, I'm aware there's a bug with him if you go into the Blackreach, where he becomes a permanent follower, which is obviously what has happened. I'm guessing that Dwemer ruin must have been attached to one of the Blackreach cells. I just want to know if there's any way to fix it.