If you mean in the TV show Bonanza then there were originally three brothers. (Adam, Hoss, and Little Joe) In later seasons however, after Pernell Roberts quit the show, Ben adopts an orphan named Jamie, so there are technically four Cartwright brothers.
Joe, Eric, Adam
On the TV series Bonanza the three sons of father Ben Cartwright were Adam Cartwright , Eric "Hoss" Cartwright and "Little" Joe - Joseph Cartwright .
There was Adam Cartwright played by Pernell Roberts, Eric "Hoss" Cartwright played by Dan Blocker, and Joseph Francis Cartwright a.k.a Little Joe Cartwright played by Michale Landon.
Nancy Cartwright is renown for voicing Bart Simpson .
It was dangerous business to be a female interested in a Cartwright man. Ben (Pa) Cartwright had three wives which all died. Little Joe married once, she died. Hoss almost married, bad luck again. It was felt that a woman would have upset the male ambiance of the show so any female love interests were quickly killed off or sent away.
Two brothers
Three brothers, Adam, Hoss and Little Joe.
Joe, Eric, Adam
Veronica Cartwright's birth name is Veronica A. Cartwright.
Herbert Daniel Cartwright.
Angela Cartwright's birth name is Cartwright, Angela Margaret.
Jesse Cartwright's birth name is Jesse James Cartwright.
Rianti Cartwright's birth name is Rianti Rhiannon Cartwright.
Rock Cartwright's birth name is Roderick Rashaun Cartwright.
Lynn Cartwright's birth name is Doralyn E. Cartwright.
William Cartwright - actor - died in 1686.
Roscoe Cartwright