When it comes to brothers fighting the most notable example is the 1993 bout between Kusuo Eguchi [江口九州男] and Katsuaki Eguchi [江口勝昭], when they traded blows for the Japanese Minimumweight title.
The bout isn't one that many will be aware of. Kusuo, who won the bout, had entered 10-3 (4) and retired in the early part of this millennium with a record of 15-12-2 (5) with 2 successful defenses of the title he won by stopping Katsuaki in 6 rounds. Katsuaki on the other hand ended his career 14-10-1 (2), with his only other bout of note being a loss to Dan Nietes, the uncle of world champion Donnie Nietes.
Despite it's peculiar place in boxing history it's a really hard fight to find thankfully however G+ will be airing the contest, along with another of Kusuo's and a little documentary, on August 2nd, between 3:15 and 4:45 local time, as they try to fill out what is other a very limited boxing schedule for the channels over the coming weeks.