Mobile issues

Hello, I'd appreciate support on the following issues with the mobile version of the site: http://www.laccla.org/ 1. The Top Menu for the mobile site is cut off: the first item (and it's 2 sub-items) do not appear. How can I ensure that all menu items appear? 2. The photos for featured pages in the featured content slider are not responsive to the width of the screen (they are responsive on my Google Pixel phone, but they are not responsive on all my coworker's iPhones). How can I assure that featured images in the slider are responsive? 3. The header video will not load on the mobile version of the site at all, so I also set a static header image as a fallback for the mobile site. However, now the desktop version of the site always shows a glimpse of that image before the video plays: is there any way to get rid of this? Thank you!