what license do i need to sell houses
You can sell your own house without a license but once you start trying to represent others who want to sell their house you need to have a licence as an agent or a broker. In Massachusetts an agent must work for a broker and to be a broker you must be an active agent for three years.
You cannot sell houses belonging to others without a Real Estate license in the State you are selling in. You need a different license for every state. You cannot obtain a Real Estate license without being a citizen of the United States. You must also be working under the guidance of a Real Estate Broker.