Early Quenya
herendo
noun. brother
heréro
noun. brother
hestaner
noun. brother
hestanoinu
noun. brother
hestanu
noun. brother
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
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).