To get the total number of online users, you can bind to a jQuery custom event named iflychat-site-online-users-count as shown below:
jQuery('#drupalchat').bind('iflychat-site-online-users-count', function(event, no) {
jQuery('#your-div').html('Online users - ' + no); //your code here
});
Your div would then be automatically updated whenever online user count changes.
Note that you should be using a premium plan in order to be able to use this feature.