Board Thread:Hints and Tips by the Mizukage!/@comment-3030647-20150902231318/@comment-1875854-20150906121758

It's not? Only the First Tsuchikage is known to be from that clan, and that was anime-only (not saying it doesn't count, just putting out there). And there's nothing that confirms the other Tsuchikage are directly related to him lol.