Adventuring Party Name Translation

Hello everyone! I'm totally new at attempting translations, so I would love feedback on my attempt.

I am trying to translate the phrase "Host of the Twilight Hall" into Sindarin. I'm not sure whether "Twilight Hall" should be in a noun-adjective structure, such as Thamas Vinuial (with Minuial mutated to Vinuial), or a compounded proper name, such as Thamuial.

I come out with Gwaith i Thamas Vinuial or Gwaith i Thamuial.

Is one more proper than the other? Am I on the right track with my understanding? Any help would be greatly appreciated. :)

For context, I am using this to describe what is essentially a fellowship (adventuring party) for a TTRPG campaign I where I will be the GM.

Thank you for your time!

I believe the structure of the name makes "Twilight Hall" into a proper place, rather than something of a noun-adjective formation. Thus, Gwaith-i-Thamuial would be appropriate. I would personally use the elided form of en, though, as it makes the connection between the adventurers and this Twilight Hall a little clearer.

The reason it's elided has to do with nasal mutation, which shortens en to e-, depending on the consonant. Since the name Thamuial begins with th, it isn't directly effected.

Gwaith-i-Thamuial is certainly an option, though Sindarin doesn’t require compounding to form a proper name, cf. Amon Hen, Minas Tirith, Nîn-in-Eilph, Ost-in-Edhil, Men-i-Naugrim, Taur-e-Ndaedelos...., in my opinion Thamuial would really just be another way to represent plain Tham Uial “Hall of Twighlight” in writing (I would prefer to spell thammuial with double m like in tham + as → thammas though, it derives from thambe < stambē). Thammas Minuial would work equally well (except that Gwaith i-Thammas Minuial would get quit long), it is however not **Thamas Vinuial, because no soft mutation happens in genitive “X of Y” constructions.

One other note though, it might be that Tolkien revised Noldorin tham, thammas to Sindarin sam as in Sammath Naur. With that change one would get Gwaith i-Sammath Minuial, Gwaith i-Hammuial.
(sammath is technically plural “all the chambers, the chamber system” so it gets the plural article in + s- → i·s-, while sam with the singular article shows i + s- → i·h-)

Thank you very much, Sámo and Gilruin, for your amazing help and thoughts!