jQuery Multiple Forms Submit

It’s not possible. You can either use serialize() or serializeArray() method for getting forms’ data and post them to the server using Ajax:

Encode a set of form elements as a string for submission.

$('#send').click(function() {
   var firstFormData  = $('form:eq(0)').serializeArray();
   var fourthFormData = $('form:eq(3)').serializeArray();
   $.ajax({
        url  : '...',
        type : 'post',
        data : firstFormData.concat(fourthFormData)
   }).done(function() {
       // ...
   });
});