How do I set validation on radio button fields?

[Beeboppaloola]

I've built an Outlook form with 2 fields containing radio buttons. I now need
to set validation on the yes/no radio buttons as follows:

Rules - form will not send unless one radio button is selected
- form will not send if both buttons selected

YesButton - on click to amend 'Send To' address from default address

Can anyone help with instructions for this vbscript?

Thanks

Bev