Select only one radio button at a time on a page with multiple radio buttons

I have a document with multiple radio buttons that need to be selected only one at a time, but now I can see that I can select all the radio buttons at the same time and I would only like for the user to be able to select one radio button at a time, which you can see in the screenshot below.

Is this possible at all, or should I convert my radio buttons to checkboxes, despite the fact that I do not like the check box style, because of the inability to make the check box itself a circle.