What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
It is not possible to add radio buttons in a group. You need to simply add check box question instead of a radio button questions. In check box question, you will be able to configure the minimum and maximum number of options that can be selected. The following guide should help you: http://www.jotform.com/help/251-How-to-set-up-minimum-or-maximum-number-of-selection-on-Checkbox-Field
Hope this helps.
Do get back to us if you have any questions.