A word for “brother” in the Qenya Lexicon of the 1910s with numerous variants: herendo or herēro, hestaner, and hesta(noi)nu, all based on the early root ᴱ√HESE that was the basis for “brother” and “sister” words (QL/40). Of these Tolkien said herendo/herēro was the “ordinary word”, and herendo appeared in the Poetic and Mythological Words of Eldarissa (PME/40).
Early Quenya
hes
noun. brother, sister, *sibling
hestanu
noun. brother
hestaner
noun. brother
hestanoinu
noun. brother
herendo
noun. brother
heréro
noun. brother
A word ᴱQ. hes in the Qenya Lexicon of the 1910s with stem form hest-. It was used as a generic term for “brother, sister”, hence = “✱sibling”, and derived from the early root ᴱ√HESE (QL/40).
Neo-Quenya: For purposes of Quenya-Sindarin, I would retain the word ᴺQ. hes as a derivative of the Neo-Root ᴺ√KHETH to serve as a gender-neutral term for “sibling”.