Many already listed but Jesus Soto Karass has a lower-level journeyman brother Jose Luis Soto Karass. Jesus isn't great but significantly better than his bro.
I think Jeff Mayweather is the inferior of the boxing Mayweather brothers, but he was still a champ!!!
Both Alvarez and Chavez Jr. have a slew of "inferior" brothers. So far for the Kameda brothers the tier goes: Koki, Daiki, and Tomoki but I'd be surprised if it stays that way when all is said and done. Tomoki has good potential, they all have opportunities, and Koki seems to be disliked/disrespected by the majority of fans so my guess is in the end one of his younger brothers will surpass him in "the public eye" of who was greater.
So according to Cliff......... He's the inferior of the two Kirkpatrick sons that became pro fighters