Howdy! BesrourMS ,
As per your requirements all you want is that, you need a bg image changed and slider to have multiple image in loop. I have gone through the file in the github.
My area of expertise are API integration, Component/module/plugin creation and modification, Theme integration, Updating your open source to the latest version, Search Engine Optimization [SEO].
Is this website developed on twig 2.x or 1.x?
Please respond ASAP, i am ready to start the work.
Thanks and Kindest regards.