Currently, there's no way to import all of your employees from Excel into QuickBooks Online. You can only import Customer, Suppliers, Product and Services, Invoice, and bills in QuickBooks South Africa.
For now, I suggest manually entering your 100 employees in the system.
Click Employees at the left panel.
Choose Add an employee.
Enter the employee's information.
For additional information, you can click this article: Add, edit, or inactivate an employee. This also provides steps on how you can make any changes in the employee's information.