You can easily add the vertical options as follows:
1)Click on the Plugins Menu on your left column menu and select editor
2) On the top right “Select plugin to edit:”
drop down menu Select twentytwenty
3) From the right side of the screen select twentytwenty/public/class-twentytwenty.php
4) Now select twentytwenty/public/assets/index.php
5) Now select twentytwenty/public/assets/js/jquery.twentytwenty.js
6) Now it’s time to edit it.
The first four lines are:
(function($){
$.fn.twentytwenty = function(options) {
var options = $.extend({default_offset_pct: 0.5, orientation: ‘horizontal’}, options);
return this.each(function() {
Where you see orientation just change “horizontal” to “vertical”
7) Click update file
All your sliders should now be vertical.
Good Luck