The Marvel Family get the new story in Shazam! 14 (Sept/Oct 74), by O'Neil and Schaffenberger.
The story features Captain Marvel, Captain Marvel, Jr and Mary Marvel, but also Uncle Dudley as well. He has no powers, but likes to dress up in a matching costume and pretend that he does. The others all humour him in this. At the top of the story, Dudley sort of helps capture a clumsy crook, and remains in his Uncle Marvel suit for the duration of the tale.
Mr Mind joins forces with Sivana, Sivana Jr and Georgia Sivana, as well as Ibac, for his new Monster Society of Evil. He has a new "death" ray, designed to channel all the evil of the members and corrupt the Marvels. I'm really not sure why they all call it a death ray when it is not intended to kill them.
Doesn't much matter, because it doesn't work anyway. The Marvels think could thoughts and hold off the effects of the ray. Then they take down Mr. Mind, Ibac and the Sivana kids. Sivana himself manages to capture Uncle Dudley and get away.
Sivana discovers that, when Dudley is asleep next to the "death" ray, the things that he dreams about get created by the ray. It does pretty much everything except kill, I guess. Dudley dreams about gryphons with Sivana heads, and Sivana sends those creatures out to attack the Marvels. The Marvels see what Sivana is doing, but he threatens to kill Dudley if they get close. So Mary and Cap turn themselves in, while Junior takes advantage of the diversion to get Dudley to read about the Marvel family, and then puts him back to sleep.
So Dudley dreams about, and the machine creates, a second Marvel Family, one in which Uncle Dudley really does have powers. The dream Marvels defeat the dream gryphons, and then Cap takes down Sivana.
Mr. Mind is back in the next issue, but Sivana and Ibac have to wait a couple of years. Sivana is next seen in this book, and Ibac in the pages of Justice League of America.