I believe that we're either missing words from our dovahzul or someone mispelt their names? (unlikely) either way, here's my thoughts on their names.

Korthor

His name could start out with Ko for within/inside or koor for summer. if it's ko then idk what the r means. the ending bit only has thur in common which means overlord. his name might be Koorthur? Summer Overlord?

Haldriin

the staring part of his name only has haal in common which means hand. the ending part could be dwiin meaning steel or there is no d and instead has rii meaning spirit or soul. So either Haaldwiin, Hand steel/hand made of steel. or Haalrii meaning hand soul/spirit? i'm leaning more for haaldwiin myself.

Akiirdal

i could only connect the start of his name with Aak, meaning guide or guidance. but the middle part fits perfectly with kiir, meaning child, maybe they shortened it so it isn't a weird long hacking sound? lastly is daal which means return. so his name could be Aakkiirdaal meaning guide child/ren to return?

Vosis

Vo means to undo, plain and simple, but sis could be siiv, to find/finding. so Vosiiv which would mean to undo finding? or as i read it, to remain lost?

Arthosiis

this was kinda hard, i would have done arth as a word, but couldn't, but Aar is a word and it means servant/slave, and adding Fo was the only way i could make the next part work as we have no tho words, or even ho words, fo means frost and siiv works for this as well, meaning find/finding. Aarfosiiv which would mean servant frost finding?

Those are all of them and i find their names really weird.

Bonus: Numinex

Nu: Now. Miin: Eye. Nax: Cruelty. Numiinnax: Now Eye Cruelty.

Hm, I have a theory.

The Dragon Priests we see in Skyrim work for Alduin, they were brought back to serve him. So, considering these Dragon Priests don't have an Alduin to serve, but they are awake, so it must be something more than just being "normal" Dragon priests.

So I believe they are from a splinter faction of priests, maybe they were too radical, and were thrown out. Therefore the names they are using are from their own Dovahzul, a separate dialect, as it were. It is still Dovahzul, just not how we know it.

Ruvgein
Hm, I have a theory. The Dragon Priests we see in Skyrim work for Alduin, they were brought back to serve him. So, considering these Dragon Priests don't have an Alduin to serve, but they are awake, so it must be something more than just being "normal" Dragon priests. So I believe they are from a splinter faction of priests, maybe they were too radical, and were thrown out. Therefore the names they are using are from their own Dovahzul, a separate dialect, as it were. It is still Dovahzul, just not how we know it.

That hypothesis might just come closest to reconciling the well researched names in Skyrim and the shoddy imitations in ESO. Well done.

Ruvgein
Hm, I have a theory. The Dragon Priests we see in Skyrim work for Alduin, they were brought back to serve him. So, considering these Dragon Priests don't have an Alduin to serve, but they are awake, so it must be something more than just being "normal" Dragon priests. So I believe they are from a splinter faction of priests, maybe they were too radical, and were thrown out. Therefore the names they are using are from their own Dovahzul, a separate dialect, as it were. It is still Dovahzul, just not how we know it.

thank you for that theory, it would certainly help :3