Is it legal for a majority owner of the family business to invest in a competitor because the competitor would sign a 5-year contract to buy products from you?
If you have a shareholder's (or other ownership agreement) in place, there may be rules about the voting percentage needed to authorize an "interested" transaction of this type (such as, simply 51 percent majority isn't sufficient; you might need 66 2/3 percent).
You have some thorny issues here and would be well-advised to speak with an attorney about your situation.
Nina L. Kaufman, Esq. is an award-winning New York City attorney, edutainer and author. Under her Ask The Business Lawyer brand, she reaches thousands of entrepreneurs and small business owners with her legal services, professional speaking, information products, and LexAppeal weekly ezine. She also writes the Making It Legal blog.