William Marshal the movie/TV show

[Sir Nate]

Maybe Charlton Heston

You are six years too late, alas!  He might've been able to pull off the Marshal nearing the end.

Well Timothy said an Actor living or Dead. But if dead then Id have to be more specific, Young Charlton Heston

[Sir Edward Oldwall]

I would suggest David Wenham (he played Faramir in LOTR). I think he could do a great portrayal of the greatest knight.

[Sir William]

David Wenham...yes, I think he could do it.  Or Sean Bean for that matter, forgot to include him.

[Sir Humphrey]

Sidney Poitier!