Dad dies and his will says that his estate goes to the four kids in equal shares. Dad has always operated as a sole proprietor. The assets of a sole proprietorship need to be specifically identified. Partnership interests present other problems. For instance, the partnership agreement itself must be reviewed to make sure it doesn't prohibit the disposition directed by the will.
Corporations also bring their own problems.
These problems can be solved with appropriate planning and drafting. If the estate is being left in trust to the heirs, beware. A business is not well-suited to being a trust investment. Investing in a family business is much less prudent than investing in publicly traded large capitalization securities. Any small business venture has a high risk.