The word G. {gwaren >>} gwarin(n) “family” appeared in the Gnomish Lexicon of the 1910s, derived from primitive ᴱ✶ŋuarenđā (GL/44). It was a combination of G. gwa- “together” and G. renni “family” (GL/65), but it is not clear why the e became i in the compound.
Neo-Sindarin: For purposes of Neo-Sindarin I would adapt this word as ᴺS. gwaren as a combination of later prefix gwa- “together” and the Neo-Root ᴺ√RE(N)D “kin”. Furthermore, I would use it specifically for a nuclear family (just the parents and children), as opposed to S. nos(s) which seems to refer to an extended family or clan.
A noun in the Gnomish Lexicon Slips of the 1910s glossed “family, etc.” of unclear derivation, though it may be related to G. eithog “ancestor, †father, sire” (PE13/113).