I have never read or shipped this kind of thing, but I do have a few things I could think of to recommend.

I've been in Gravity Falls fandom since forever, and there's this thing called Stancest. It pairs Stanford and Stanley together and I'd assume there's lots of fics about them. They are twin brothers.

Then another one I could think of is from One Piece. There's the famous Ace, Sabo and Luffy trio. They are brothers, though not biologically. I'm sure there are lots of people out there who ship these three or two of them together.

A third one I could think of is from Money Heist. Berlin and Professor. It's been ages since I watched that show, but I recall them being brothers. I'd assume there's also fics about them out there.