1. Call Max Schechner - 781-935-1818. He is a real estate attorney who specializes in conversions.
2. He will recommend an architect who has to draw simple plans.
3. You will need to make sure you have utilities properly separated.
4. Assuming you are doing this to sell one or both, call me for values!
Your first call should be to the zoning board to see if your property is zoned to allow for the conversion, then the building department for any minimum requirements you'll need to meet to satisfy them. Then consult with the attorney to flesh out the rest.
Good luck, hope that helps