Hello,
You need to add the images while adding variations inside the variation tab option as in the screenshot: https://www.screencast.com/t/05qDwRHu24Z
I have created a variable product as an example you can see the screenshot: Without Variation selected https://www.screencast.com/t/3Zm9PH5fY
With variation selected: https://www.screencast.com/t/9ewSOdO29U
To add multiple images for each product variation see the screenshot: https://ibb.co/K7j1QBB
I also visits your site and notice the you are using some image for variation gallery but they are not showing as expected. Could you please deactivate all the third party plugins, switch to parent theme, remove your custom CSS code and then check back after clearing your site and browser cache.
In case if the issue is still there then remain the plugins as disable and let us trouble shoot with theme default plugins.
Best Regards.