I have two male cats, not related but they're bonded very closely like brothers. They have never had a serious fight, both have their claws intact as well. They're two weeks apart in age (brought home seperately two weeks apart) and were neutered at six months on the same day.
Both of my sisters have a female cat, littermates and they lived together until they were about 1.5 and those two cats have had so many fights it's not funny. Both were spayed on the same day at 6 months, and thankfully they're both declawed or I'm sure both would be carrying some nasty scars
Needless to say once my two are gone I'm going back to just one. I've been really fortunate with my two but I'm not risking any cat fights
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - male GSD - born Jan 26, 2012
Koda & Zazu - 4 year old male cats