How do shares of ownership work in an LLC-S corp ?

An LLC is not a corporation and it generally does not have shares; it has membership interests, which are very similar to partnership interests. They are generally evidenced solely by book entries in the LLC's records and are generally not evidenced by certificates, as one might expect with shares of a corporation's stock, although the operating agreement of the LLC may provide for certificates (which is rare). LLCs do not have "shares" and the ownership of a majority of the membership interests does not import any special rights unless provided in the operating agreement. The rights of the members are governed by this operating agreement, and you should refer to it for your rights and privileges. From the description you give, no member is a "majority" member because no single member owns more than 50% of the membership interests. S corporation status is merely a tax election (which can be made by entities that are not corporations, such as an LLC) and imports no particular rights or liabilities as against the other members.