It's quite clear that they don't entirely know what to do with themselves at first! Then Dino starts clowning around, Sammy joins in, and before you know it the pair of them are doing a take on the Martin & Lewis act, which was then of course still underway. Well worth a listen. Whether or not this is the first recording of Frank, Dino and Sammy together on stage I don't know, but it's certainly the earliest that I've heard.
Thank goodness for handy people with tape recorders! ;)