Hello there!,
Well, the warnig of the not safe stuff should be because of the SSL certificate, the video thing, well, I gotta take a look at the site first and see what happens; Do you know if the problem happens only on phones? or also on desktop?
About the slides, again, I should take a look, maybe it will be just a matter of resizing the images, or could be something else!.
Cheers ~