I've seen the brothers thing work amazingly well for party unity in D&D games, but party unity isn't quite the same thing on CF. So, largely the reasons others have given say why it's bad.

But, it brought to mind an example of two brothers from CF past. In this case it worked well, especially since they didn't know each other out of character. They were brothers because their mentor ended up adopting both of them. Although they were friends and cabal-mates, they almost never grouped, and didn't even care to stay within range to do so much of the time.

However, the part that worked especially well was the legacy that grew from there: An entire family line. I almost joined it twice, but I wasn't ready. The adoption method largely bypassed the need to have OOC contacts, and skipping a generation before playing another family member avoided needing direct knowledge of previous characters. I'm not sure the Imms would like the idea now, but it worked great then. Probably because the members tried very hard to keep it a solely IC thing.

BTW, the brothers were Darwin and Daeldron Windgust.