It may be that Moroni is not giving, nor did he necessarily intend to give, a complete genealogy of Ether. This would possibly explain why he uses “son of” in some cases and “descendant of” in others. It may be that to save space, he is merely illustrating the several generations that span from Jared and his brother, at the time of Babel, to Ether, the last of the Jaredite prophets.