Hello @erreid,
As far as we have checked the issue locally, all of the four slider is displaying as well as working fine .
So can you post your site URL so that we could properly inspect your issue?
Also according to the theme feature number of slides can be set to four. And to increase the no. requires a higher code customization which is beyond the support we offer for our product .
So you can hire a professional developer .
To hire a developer please follow the link below
http://themepalace.com/hire-a-customizer/
We hope it helps,
Best Regards!!