Check boxes. How to prevent others from checking when one is already checked?

Sorry to be a nuisance but I have a submenu of checkboxes in one of the expandable areas connected to the one of the main menu checkboxes. I want these buttons to be clicked and unclicked the same way as the others, but if I connect them to the same Currently Checked Box function, when checked, it will close the expandable area it is in as well. So I created another function for this submenu and did the exact same setup as previously. It doesn’t work. Am I thinking in a wrong way here?