Primary Coverage with Immediate (-I) Ring is what you want, but you can only put one cover button for an extension on another extension. That is, you can't put multiple cover buttons for 101 on 102. However, you can also put a pickup 101 button on 102. Then, when the cover 101 button rings, press the pickup 101 button to pull the call over to your own SA button, leaving the coverage button free to ring for another call.