These videos come from a National Lampoon stage show, Lemmings, with John Belushi, Chevy Chase, and Christopher Guest, among others. I owned the soundtrack many years ago.
Belushi lures "Bob on stage to perform:
Belushi introduces Christopher Guest who parodies James Taylor:
Belushi (with a faux Leon Russell) performs his very good Joe Cocker parody:
A Crosby Stills and Nash/San Francisco sound parody:
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