I've never tried to raise an orphaned litter, but from my reading on RT, I know that you should mix the goat milk replacer at double strength. Kits aspirate fluids easily (breathe it into their lungs, causing pneumonia if not immediate drowning), so do not force the liquids into them. Go slowly. Keep them warm and make sure to stimulate them with a warm damp cloth to make them relieve themselves.
Even with the best of care, mortality is very high. The best way to save the litter would be to foster them to another rabbit.