Is this Shemayah mentioned above (4)?
Radak: Yes, he was Yo'el's son.
Malbim: No, it is Yo'el's great grandson Shim'i.
Why was he in "Aro'er"? It is not part of Reuven, rather, of Gad - "va'Yivnu Vnei Gad? v'Es Aro'er"!
Radak #1: The prefix Beis is in place of a Mem. We find like this - "veha'Nosar ba'Basar uva'Lechem", "va'Yrotzezu? ba'Shanah ha'Hi Shemoneh Esre Shanah."
Radak #2: He dwelled on the border of Aro'er. The city was of Gad, but its border was of Reuven.
Malbim: In the days of Sha'ul, they fought with Bnei Hagar, and widened their border to the east (10). Ezra teaches that then, they made a new division. Bnei Gad gave Aro'er, from their portion, for Bnei Reuven could not spread far past their border, due to the Pras river - "vela'Mizrach Yashav Ad Levo Midbarah l'Min ha'Nahar Pras" (9). Therefore they gave Aro'er to Reuven, and Bnei Menasheh spread past their border to Senir. Initially their border was only until Chermon; later, they increased and extended it towards Damesek. They stretched their border mostly towards Gil'ad. The primary Gil'ad was of Menasheh - "vela'Machir Nasati Es ha'Gil'ad." Bnei Hagar were east of Gil'ad - "va'Yeshevu b'Ohaleihem Al Kol Pnei Mizrach la'Gil'ad." Menasheh received most of the new conquest. They needed to divide again to equate the inheritances 1
If all fought together, they should all divide the added land. Reuven could not take [much] from the added land, for it was not connected to their portion. (PF)
What is the meaning of "v'Ad Nevo u'Va'al Me'on"?
'Rashi': Initially, before they came to Yisrael, they were called Nevo and Va'al Me'on based on their idolatries. Idolaters called idolatry on the name of their cities. When Yisrael captured them, they changed the names - "Nevo v'Es Ba'al Me'on Musabos Shem" (Bamidbar 32:38). They did not change the name Sivmah (ibid.), for it was not based on idolatry; Nevo and Va'al Me'on were names of idolatry (Megilah 25b).
