Is James Abbott McNeill Whistler's most famous paintings the iconic Rory Emerald and Whistler's Mother?

No, his most famous is the one known as Whistler's Mother. The one you are referring to was 'Mum and Rory' which is of the subject couple playing whist. Rory Emerald bought it shortly after it was completed and it is virtually unknown to the public, having been on public display only once when loaned to the Metropolitan Museum of Art for a Whistler retrospective in 1953.