Why does it say "u'Vnei (plural) Eisan"? It lists only one!
'Rashi', Radak: Sometimes verses use the plural for one, e.g. "u'Vnei Dan Chushim", "u'Vnei Falu Eli'av 1 ." Also refer to Bereishis 46:23:1:1-4 and the notes there.
Malbim: Ezra copied his Sefer from the great Sefer of lineage, which had the lineage of every family and its branches, from beginning to end. He copied only what is needed, and special people. The great Sefer listed many Bnei Zimri, and among them Karmi. It listed many Bnei Karmi, and among them Achan. Ezra wrote u'Vnei, like it said there.
Malbim (here and Bamidbar 26:8): The plural always teaches more than one; sometimes there is a reason to list only one. Later, Dan had other sons; the verse listed only those who descended to Egypt. Falu had other sons; some say that he is Peles, Ohn's father. Only Eli'av is listed, for the next verse teaches that Dasan was his son.
Why did Ezra not record the sons of Heiman, Kalkol and Dara?
Radak #1: He did not find them.
Radak #2: He was concise about Zerach's seed, for kingship does not come from him. He elaborates about Chetzron ben Peretz, for kingship comes from him.
Malbim: The great Sefer of lineage listed many Bnei Eisan. Ezra copied only the first; he wrote u'Vnei to hint that there were more sons. In Sefer Ezra (4:17, 7:12) he wrote Shlam or Gamir (they are like etc.) in place of writing all the names.
