Merge values from two forms on submit

jQuery serialize supports multiple form elements, So it is possible to do:

$('#form1, #form2').serialize();

And for your case, you can do:

$('#form1').submit(function() {
    var action = $(this).attr('action');
    if (!EntryCheck()) return false;
    $.ajax({
        url  : action,
        type : 'POST',
        data : $('#form1, #form2').serialize(),
        success : function() {
            window.location.replace(action);
        }
    });
    return false;
});