So many considerations.
What are the results of the objective assessments. Do any one of them have any diagnosed clinical conditions. If so that changes the game.
Remember, obesity is a CLINICAL condition. It is a DISEASE. Does Dad have hypertension, diabetes, high cholesterol if so you can’t treat them the same.
I don’t know enough about the clients to give a safe suggestion.
Everyone responds to exercise differently depending upon their level of conditioning.
Best to you.