Glad I was able to help you earlier, and thanks for writing back.
From some research (make mutually exclusive checkboxes in a pdf search query), it looks like you can make this happen by ensuring all the related checkboxes have the same name, but a different export value.
You can check & set both of these values from the Properties menu.
Go to Forms, Select Fields.
Select your fields.
Change the name of the fields in the box that shows up on the far left corner (Name:).
Then click on each field in that group, go to Properties, Properties (or right-click and choose Properties).
Go to the Options tab, and change the Export Value field to a different value.
Repeat for each field in the group.
When you test, you'll now see that clicking on a checkbox in that group will check a box, but not allow you to do a second check in that group. You can also uncheck everything in case you've made a mistake.
Good luck, and thanks for your question!
Check Boxes will act like Radio Buttons if they have the same name but
different export values. The export value is set on the “Options” tab of the Check
Box’s Properties Dialog.