Bros. is a short written form of Brothers. You see it in company names, not in ordinary sentences about your family. Warner Bros. is the famous one: it started as a business run by brothers, and the short form stayed in the name. You will also see names like “Smith Bros.” on shops and old signs. It is a writing habit, mostly in American-style names, and it usually keeps the full stop. It is not the same as bro or bros in texts between friends — that slang is a later, looser use of the same family of words. When you see Bros. on a building or a film logo, read it as “Brothers.”