Why does it say "v'Shem ha'Ish
Malbim: He was known, and also his wife and sons were famous. He left, lest the commoners demand from him to feed them. And this is why he was punished - when he left, Yisrael's hearts fell, and also there was Chilul Hashem.
Here they are called Machlon and Kilyon. In Divrei ha'Yamim I, 4:22 they are called Yo'ash and Saraf!
Torah Temimah citing Bava Basra 91b #1]: Their names were Machlon and Kilyon. They are called Yo'ash and Saraf because Nisya'ashu (they despaired) of Ge'ulah, and they were worthy to be Nisrafim (burned).
Bava Basra 91b #2: Their real names were Yo'ash and Saraf. They are called Machlon and Chilyon because they made themselves Chulin and were worthy of Kelayah (eradication). Vilna Gaon (5) - what is the source that both names apply to both of them? "Gam Sheneihem Machlon v'Chilyon" teaches this.
What are "Efratim"?
Rashi #1: They are important. This is like "Ben Tochu ven Tzuf Efrasi" (Shmuel I, 1:1). We find that Eglon married his daughter to Machlon - Rus was Eglon's daughter 1 .
Rashi #2: They were from Beis Lechem, which is called Efras. Malbim #1 - initially it was called Efras. Afterwards it was called Beis Lechem - Efras. Afterwards it was called Beis Lechem - "va'Ekbereha Sham b'Derech Efras Hi Beis Lechem" (Bereishis 48:7).
Malbim #2: It is a family among the best lineage of Shevet Yehudah. They are called Efratim based on Kalev's wife (Efras - Divrei ha'Yamim I, 2:19); she was great and esteemed.
Nazir 23b: She was his son's daughter. Tosfos (23b) - really, she was several generations after Eglon. Ivtzan (Bo'az) was 200 years after Eglon, and Rus converted in her youth! (Rus Rabah - she was 40 at the time.) Some lived more than 300 years in that generation (refer to 2:1:1:1*)! Perhaps Tosfos holds that Goyim would not live so long. However, some Goyim lived hundreds of years, e.g. Og, Pharaoh and Iyov! - PF)
What do we learn from "va'Yavo'u Sedei Mo'av va'Yihyu Sham"?
Vilna Gaon: They left Eretz Yisrael because they were stingy about Aniyim. They went to Mo'avim who were also stingy - "Al Davar Asher Lo Kidmu Eschem" (Devarim 23:5). Once they came there, even though they were strangers, and did not have the nature of the residents so much, their nature became like the Mo'avim.
Malbim: Even though initially they intended to go temporarily, after they got there, "va'Yihyu Sham" - they decided to live there on a fixed basis.
