Doing things dynamically on a page requires JavaScript in order to "pick up" on an event happening on the page (mouse click, etc.) and then do something in return (find the radio button with a specific name and set it to checked). In order to do something like this in SSI Web, you probably would need to use a free-format question so that you can add event listeners to the various radio buttons, and then write some code that said "If the third radio button for Q1_r1 is selection, find Q2_r1 and select the third radio button as well."