I don't have much time, so i'll keep it simple.
Kazek Jharo and Zerik Jharo are brothers (and the people in charge of Jharo Brothers Munitions)
Gnarko has a cousin named Gildaro, who is NOT a drunkard.
Gnargle Toothface and "The Skeb", also known as Edzgota Smulhed, are technically brothers, though nobody really cares, cause they're skeb.
Skeskin and Skeltan are (currently) brothers, but that may be subject to change, as they are not terribly developed yet.
And then there's all the friendships and other relationships, but that's a tangled mess that you wouldn't want to attempt to understand.