What theme is this?

Try using https://whatwpthemeisthat.com/

Knowing a theme doesn’t always tell you much. In the caase of Kelton Global, they are using a heavily modified theme of Twenty Twelve.

They put it in a directory called “/kelton”, yet it’s style.css still lists it as Twenty Twelve: https://keltonglobal.com/wp-content/themes/kelton/style.css

So while it may give you an idea what theme they’re using, sometimes it’s just a starting point for them. The looping video could be either a plugin or something they coded themselves.

Cantina uses a modified TwentyThirteen. Might be a child-theme even, but it seems they simply copied twentythirteen and modified it, just like Kelton.