A while back, I rediscovered this group from the 60s that I had forgotten about and was amazed to see that they had an accordionist. So I did a little research. All is not what it seems. See:
https://en.wikipedia.org/wiki/Gary_Lewis_&_the_Playboys
In all of their television appearances, they are pretending to play their instruments and lip-syncing to studio recordings. These studio recordings were heavily overdubbed by session musicians, the group known as "The Wrecking Crew". It is probably Leon Russell of this group that you hear playing the keyboard parts. That is how the "sausage was made" back in those days, as record producers did not want to take any chances or waste expensive studio time with inexperienced musicians. Even Gary, who you do hear singing, had his vocals doubled by a session vocalist on many of these recordings.
It would be fun to hear this group before they were "discovered" and given a recording contract. When they were just a local band playing gigs in their neighborhood, you would have heard John West on his Cordovox. I searched but have not found any recordings or film of this time.
Gary was the oldest son of comedian Jerry Lewis. Kind of sad and hard to understand, but Jerry disinherited Gary and his other sons from his first marriage.
Gary Lewis and the Playboys live on. Gary is doing concerts to this day with a different band, but unfortunately, no accordionist.
www.garylewisandtheplayboys.com
Here are his hits from the 60s performed at a concert in 2004. No lip-syncing here, it is all live.