only one info ballon can be open at a time, you wont be able to have them both open.
to have one open, find the three isntances of the following code:
if('address_1' == 'address_0')
marker_1.openInfoWindowHtml(address_1.infowindowtext);
and change it to:
//if('address_1' == 'address_0')
marker_1.openInfoWindowHtml(address_1.infowindowtext);