Quenya for Gown of House Feanor

Best I can come up with is:

Nampënisseo Nossë Fëanor

Last one for a while! Comments?

Some comments.

• Feanor is the Sindarised version of the Quenya name Feanáro; that is to say, Feanor is not Quenya, and not really proper Sindarin either. Definitely avoid it in Quenya; in Sindarin I would suggest using the proper Sindarin form Faenor (attested in Morgoth's Ring p. 217).
• The diaraesis is misplaced in the first word of your attempt (which admittedly I am not sure how you formed, see below for an alternative). The diaraesis is an optional diacritic (note that I did not use it above) which Tolkien used in Elvish to signify that a vowel is syllabic, for ease of reading. Thus it is only used on final -e vowels of polysyllabic words (because in English the final e is normally silent, so he felt the need to clarify that in Quenya it isn't), and for vowels in hiatus (two neighbouring vowels that do not form a diphthong), as in Fëanor. As such your word should be nampenissëo (if it was a correct word), or without any diaraesis at all.
• You attached the genitive case to the wrong word (and it may not be the genitive case that you need here to begin with).

Now as for "Gown of House Feanor" - I am not entirely sure what exactly you mean by this. But I'll assume this is meant to be [some] gown that belongs to or is attributed to the House of Feanor. For "gown" I would use happa, a neologism suggested by Luinyelle from Vinye Lambengolmor.

Thus we get happa nosseva Feanárova.

Alternatively, if it is [some] gown that was given by or made by the House of Feanor [to someone else], i.e. a gown that is not owned nor attributed to the House of Feanor, then you should use the genitive case: happa nosseo Feanárova.

I'm sorry about that. The moment the bots realised we have bot protection, it seems that they've resorted to LLM spamming (like ChatGPT.) Running a website nowadays is such a chore. 😭