Give them one question and 5 minutes to answer. Have each answer it. Allow a 2-minute rebuttal. For 8 candidates, that would take an hour. Then allow re-rebuttals, ad infinitum. Cable TV news is not so inflexible that it cannot give these guys 2 hours, 3 hours, till the cows come home hours.
Give them the question in advance so they can answer precisely how they feel.
Let them take potshots at one another.
Let them say whatever they want.
Then, when they are finished, politely thank them for their time.
Quit having the tail try to wag the damned dog.