Rashi #1: He was from Beis Kel. This is like "Yishai Beis ha'Lachmi", "Yehoshua Beis ha'Shimshi" (Shmuel I, 15:1, 6:14) and "Efras Avi ha'Ezri" (Shoftim 6:24); it does not say ha'Avi Ezri.

Rashi #2 (from Sanhedrin 113a), Targum Yonasan: It is because he accepted the curses (Alos) of Yehoshua (whoever will rebuild Yericho

Rashi citing Yerushalmi Sanhedrin 10:2: We attribute the curse to the one who perverted his ways (alternatively - is messed up).

Radak: He was under Achav's jurisdiction, and Achav did not protest. He was so evil; until him, no one considered rebuilding Yericho, due to Yehoshua's curse.

Malbim: Even though they served the calves, they did not yet cast off the roots of Emunah; they feared Yehoshua's Shevu'ah and curse. Now they saw that Achav does all abominations and Hashem does not punish him, so they denied Hashgachah and Nevu'ah, and were not concerned for Yehoshua's curse. Therefore, he built Yericho. Even though he saw that Yehoshua's curse was fulfilled on his son Aviram, he did not put his heart to this and attributed it to chance, until he erected the doors and his last son died.

Radak: We find like this, e.g. "Ohalo" (Bereishis 9:21, 12:8) and similar verses.

Rashi: When he made the foundation, his firstborn son died. He buried more sons [while rebuilding Yericho], until his last son died when he erected the doors, just like Yehoshua's curse (Yehoshua 6:26).

Radak citing Targum Yonasan: He killed ¹ Aviram his Bechor when he made the foundation.

Radak: Aleph, Hei, Vov and Yud are interchangeable. We find that Pa'u (Bereishis 36:39) is called Pa'i (Divrei ha'Yamim I, 1:50), and Alvan (Bereishis 36:23) is called Alyan (Divrei ha'Yamim I, 1:40).