Robin is ticklish-on the Christmas tickling show Jackie breaks into her booth and starts tickling her-Robin shrieks and tells him to get away "I hate being tickled!" and then Fred chimes in with "Oh, she is SO ticklish." Furthermore, it appears that Howard removes her shoes and tickles her foot in a scene from Private Parts. Robin herself mentioned this in an interview (according to the Ironic Tickler's ticklish celeb list).
As far as Lily is concerned, I believe that girl to be hyper ticklish! One of the most of all time!! And add Tracy and Starr to that list as well!