Fire event of Checkbox

Why do you propose to do that? The only sensible way to do that is to change the Checked status of the second CheckBox in the event handler for the first. Note that this may require a real change: true <->false rather than "myCheckBox.Checked = true;" as the changed event may not fire if the Checked state is true before you set it to true.

The better way would be to put the relevant code into a separate method you can call from both handlers.