IS THAT GRAMMAR CORRECT?

The manager has done the risk management to staffs to decrease the risks happened monthly who also hold a meeting to tell staffs how to handle new risk in the center. After few months, the general manager hold another meeting about some case studies to teach staffs what is the best solution.
Manager will improve and increase the manuals of guideline so as to increase the knowledge of safety to staff and comply with all safety rules.

staff 不可加 S。

The manager has done the risk management to the staffs in order to reduce possible risks. The manager holds a meeting every month to inform the staffs how to handle new risk in the center. And, the general manager holds a quarterly case study meeting to educate the staffs for the best solution.
Manager will update the guidelines of the manuals to enhance the safety knowledge to the staffs and to ensure the staffs comply with all the safety rules.

The manager is carrying out risk management for the company to reduce risks that happen from time to time. He / she held a meeting in the center to teach the staff the ways of handling new risks. Quarterly, the general manager holds a meeting about case-studies and tell the staff what the best solutions are. The Manager will revise and update the operational manuals / guidelines, which will increase staffs' safety knowledge and enable them to comply with all safety rules.