As stated above, the sons would have to start a new business. In my opinion, this would be a good thing. The sons could start a partnership. The sons would probably not have to pay business income tax under a partnership and it would open the door to discuss just how the business is going to be run in dept. They would have to determine how the income, work and contributions are broken up and this could be a good way to go into a company on a good foot. It might also create conflict but if two sons are going into a business together, they have to be able to communicate enough to be able to determine how they want the business to be run.
http://info.legalzoom.com/can-sole-proprietorships-multiple-owners-23282.html