mother/daughter to legal 2 family

[SUSANA PARRALES]

I have a Mother/Daughter home in Middlesex, NJ that has a separate, private entrance for the second floor apartment. It has it's own kitchen, bathroom, 2 bedrooms and living & dining. It's about 900 square ft, built in 2007. It has its own separate heat & airconditioners with separate controls for each floor, but the utilities are all one electric, one gas and one water bill. I want to find out if it is possible to convert to a legal two family home, how much would it cost and how much more value will the property go up as a legal 2 family home. Any advice?