This may be a little to simple.
How about 3 @ 4" elbows, on 3 overflow pipes, output pointing up. This would make most of the available water go out 1 left 4" pipe, but if the flow is too much, it could still get out the 3 elbows.
Then a 4x2" (or 3") reducer, to 20' of 2" (or 3") pipe down to the 'genny'. Measure the head.
See how long it takes to fill a 5 gallon bucket.
I doubt it would effect the home water supply. Could cut the top half of the end of a 4" cap off, put it on your 'power pipe' to allow the homes to get first dibbs, you get next dibbs, extra still goes out the overflow?
You could assume it would work and build a matched system here to take with you.
Furnace blower and matching nozzle, TDMs / treadmill motors, assorted pulleys, whatever...
Would the neighbor who owns the spot 20' down the hill really care about a 2' box up there? I wouldn't.
Stray thoughts...
G-