1)
Why does it say "v'Galelu"?
1.
Rashi (based on Targum Onkelos): They used to do so regularly.
2.
Ha'amek Davar: They said "they roll" (and not 'we roll') because they were only three, a minority of those who roll it. It says "v'Hishkinu," for each gave to his own flock to drink.