How do I prevent form submission until multiple ajax calls have finished? jquery

Following on from a previous question where I asked about disabling a submit button until all ajax calls have finished returning...

It seems that people are still managing to submit the form even with the button disabled and a warning sign. I guess it could be from pressing 'enter' in a text input.

How do I go about disabling the whole form, rather than just the submit button?

The code so far is:

// if we're waiting for any ajax to complete we need to disable the submit
$(document).ajaxStart(function() {
  $(".ajaxbutton").attr("disabled", "disabled");
  // if it's taken longer than 250ms display waiting message
  timer = setTimeout(function() {
    $('#processingAlert').html(' ...please wait one moment');
    $('#processingAlert').show();
  }, 250);
})
$(document).ajaxComplete(function() {
  $(".ajaxbutton").removeAttr("disabled");
    $('#processingAlert').hide();
    // cancel showing the message when the ajax call completes.
clearTimeout(timer);
});

One other thing that I should mention which could be causing a problem is that there are multiple ajax calls happening at the same time, EG one div receives hidden inputs and another div elsewhere on the page shows a price total for instance.

Would the fact that some ajax calls are completing quickly negate the disabling effect of ajaxStart? EG ajax call1 and ajax call2 both fire the ajaxStart - call1 finishes really quickly, would it re-enable the form while we are waiting for call2 to complete?

Is there a better way of doing this where we could simply test if ALL ajax calls have completed?