Hell in the Pacific, Enemy Mine, Milo and Otis(yes I know about the horror), The Incredible Journey, Arashi no Yoru ni, Cast Away, The Old man and the Sea...
Shit I know most are doubles and there are other people in them but for the most part they are two character movies. Hell some of them are about animals walking. I'm sure there are more but a good movie could be made without people. Call it nuance or some shit. I know there are others as well. Just can't remember them off the top of my head.
Still the two character would be the alien and the predator. Basically men in rubber suits. It can be made to work. There can be people, in the way, but not important.