1)
Which water did they seize?
1.
Rashi: It was the water (river) separating between Aram 1 and Eretz Kena'an. Also the Yarden separates.
1
Presumably, Rashi assumes that Midyan dwelled in Aram, for Bil'am lived there (Bamidbar 23:7). Refer to 6:2:1:1-3. (PF)