JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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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.
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