@Nancy, after inspecting your site from browser source code it appears like you have inserted the video twice in Sidebar Frontpage Widget Area as a result there is double video on your front-page. So please verify and if exists, please remove the one and it should be fine.
Next regarding 404 page, we tried to access the posts and pages from homepage and they pretty working fine as expected.
However, if still the problem exists go to Settings -> Permalinks and [Save] the settings without any change in option and it should work.
Let us know how it goes.