I have an Extreme brush which is narrow enough to fit and clean above that vent.
With that number of windows my first run would be to just clean above the vent only and each side of it with a lower flow and move onto the next one. Drop down and do the next floor etc.
Once you have done, or done enough for the first vents to have 'dried' off a bit, then wash the rest of the window below the vents on the second run.