Without any qualifiers or any other clear context, it would not be clear that you mean only a portion, and not all. I wouldn't say "I sold my house" if I only meant I sold one room of my house.
So again, you should state clearly that they would have to sell a share of their company, not the company itself.
Or if the company does not want to issue equity interests to outsiders, then maybe they would have to sell certain assets belonging to the company to pay taxes but they again would not be selling the company itself.