I'm redoing my bathroom, I bought a light/fan/night light unit and need to wire it into the existing light. I only have hot & common wires and power goes to light first, the night light has to be separate. How do I wire the fan and light using the existing wires but to 2 switches?

Unless you have a 3 conductor wire, you can't do it. With 2 separate switches you need to run a 14/3, 1 neutral, 2 hots, 1 ground. If you are redoing the bath, it shouldn't be too hard to run another wire.