Is "My brother, who lives in Mumbai, is an engineer" correct?

Why

Kartik is treating commas the way they're sometimes used elsewhere, as a matter of pacing or style that doesn't touch the actual meaning. Around a relative clause like "who lives in Mumbai", though, commas carry real information. WITH commas, as Kartik wrote it, the clause is treated as EXTRA, non-essential information — the sentence is really saying "my brother is an engineer" and just adding a side-note about where he lives, which only makes clean sense if Kartik has exactly ONE brother, since "my brother" alone already identifies who's meant. But Kartik has two brothers, so "my brother" alone doesn't say which one — the clause "who lives in Mumbai" is actually doing essential identifying work, telling the reader WHICH brother is meant, and essential, identifying clauses like this should have NO commas: "My brother who lives in Mumbai is an engineer." Test: read the comma-version aloud to someone who doesn't know Kartik has two brothers — they'll assume he has only one, because that's exactly what the comma version signals. No, the comma changes the meaning: without commas, the clause identifies WHICH brother; with commas, it assumes there's only one and adds a side-note — and since Kartik has two brothers, the commas here are actually misleading.