Why would "Helaman, who was the son of Helaman," be "appointed to fill the judgment-seat" (Helaman 2:2)? According to Michael Hobby, apparently the laws instituted by Mosiah2 had provided that should there be no heir for the judgment-seat, the Nephites would be ensured continued control in that it would automatically revert to the High Priest, as it had initially begun (see Mosiah 29:42). From that point, it would again pass by right of lineage. Therefore, the Nephites placed the High Priest, Helaman3 , son of Helaman2 , in the seat. [Michael M. Hobby, The Mulekite Connection, p. 46]
Helaman 2:1-2 Helaman, who was the son of Helaman, was appointed to fill the judgment-seat (Nephite Chief Priests) [[Illustration]]: Nephite Chief Priests. Adapted from [John W. Welch and Morgan A. Ashton, "Charting the Book of Mormon," Packet 1, F.A.R.M.S., 1997]