1)
Why did he put them in Beis Kel and in Dan?
1.
Radak: He said that Beis Kel was chosen, like Yerushalayim; Yakov said about it "Yihyeh Beis Elokim" (Bereishis 28:22). He put the other in Dan, at the [northern] border 1 of Eretz Yisrael, like it says "mi'Dan v'Ad Be'er-Shava" (5:5).
2.
Malbim: It was so everyone could go to the one closer to himself.