You could use several different double loop knots like the spanish bowline or bowline on a bight. Either would make the two leg loops. You could add a half hitch or french bowline around the chest. Alternately a fireman's chair knot tied in the middle of a line would allow you to lower someone with one end of the rope and control the descent with the other end.
Woody
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"Crystal clear on logic but short on expertise" - James William Buffett