I copied the solution from link: http://stackoverflow.com/questions/19305821/multiple-modals-overlay
$(document).on('show.bs.modal', '.modal', function () {
var zIndex = 1040 + (10 * $('.modal:visible').length);
$(this).css('z-index', zIndex);
setTimeout(function() {
$('.modal-backdrop').not('.modal-stack').css('z-index', zIndex - 1).addClass('modal-stack');
}, 0);
});
Scrollbar fix
If you have a modal on your page that exceeds the browser height, then you can't scroll in it when closing an second modal. To fix this add:
$(document).on('hidden.bs.modal', '.modal', function () {
$('.modal:visible').length && $(document.body).addClass('modal-open');
});