As it is your family business, you may have access to the secretarial records maintained by the company. In such case, you can see the Annual Return of the Company filed every year to confirm whether you are a shareholder. This is an authenticated way of confirmation of your status.
It is mandatory to disclose the names of all the shareholders who hold more than 5% of the total share capital of the company in the audited financial statements. As you hold 33.3% of the shares of the company, your name should have been disclosed in the audited financial statements. You may check this out from the audited financial statements, under the note relating to Share capital.
