Ive attached a WebForms .package (renamed as a .zip) that shows what I'm doing (ignore any warning that says it was done in a later build). I've done it for the 3rd radio button set in the list... here's a series of steps:
1. Give the radio buttons Control IDs (under Functionality/Behavior) of "rad1", "rad2, and "rad3"
2. Add an AttributeKeyValuePair custom even to the third radio button "rad3". Make it an onclick event, and use the following script:
var radio110 = document.getElementById("rad1_l_0");
var radio111 = document.getElementById("rad1_l_1");
var radio112 = document.getElementById("rad1_l_2");
var radio210 = document.getElementById("rad2_l_0");
radio110.checked = false;
radio111.checked = false;
radio112.checked = false;
radio210.checked = false;
And that should do it. You should be able to use the above to do the same for the first two radio buttons as well. Notice the radio button item elements have IDs that follow the format of <control ID>_<lower case L>_<0-based index of item>. Thus, your rad3 item elements would be rad3_l_0 and rad3_l_1.
Hope this helps. If you have any questions, fell free to ask.