You won't get 4V with darlingtons. If the current isn't too high simple BJT's will work (you'll also
need 4 freewheel diodes for them). BJTs in saturation will get to 0.2V perhaps, the high side one's
cannot saturate if NPN though, will need to be PNP (and need base resistors and will be inverted
drive).
You haven't told us what the load is yet.