you can run 2 off one pump but.....
try and split flow equally between users.
as for the varistream it should work, but the setting would need to be turned up.
ideally, it would be better to use 2 pumps and varistream, but if money dosnt allow, then one can be used. 1000 ltr tank in van, are you doing commercial? if so, i would say you would def be better with 2 pumps, at least then, if 1 pump goes down, you can run 2 operatives off 1 pump.