Dear Kathy,
Just because 3 out of 4 shareholders have a benefit does not mean that the 4th shareholder must receive something for it. That determination, if not covered under corporate Bylaws or Articles of Incorporation or other agreements, is entirely up to all 4 shareholders to decide how or if they want to do something about it.
The sharing of profits, losses, or benefits in a corporation, whether a C or S corp., is determined by the shareholders (owners of the corporation) and the corporation's Bylaws or Articles of Incorporation. If the Bylaws and Articles of Incorporation do not spell out how to handle this situation, then the shareholders can simply meet to discuss who should have benefits paid by the company, in what manner, and vote on that issue.
The election to offer health insurance is a private decision by the shareholders and, if under Bylaws or Articles of Incorporation, the decision requires a vote, then the vote is determined by the ownership percentages of each shareholder. An accountant should be consulted to see if there is anything the company can do in such a situation to benefit itself and the shareholders (i.e., whether from a tax perspective offering benefits to all or some other compensation would be good for the company or shareholder).
PLEASE NOTE: Responses here are for information/education only, NOT legal advice and do not form attorney-client relationship! Only licensed attorneys you hire in your state can provide legal advice.