會計帥樓係咪唔可以上市？

Account firm, I assume you mean a CPA (Practising) Firm. A CPA organisation structure is now could be a sole proprietorship, partnership or even a limited company. A CPA firm could not be listed in the stock market.

Because of conflict of interest. If aaccounting firm can, lawyer firm also can. That could voilate the Hong Kong regulation of law.

Account firm and Lawyer firm are the kinds of partnership. This is the company law.