I am trying to make a decision on whether to sign up for a
Catastrophic Medical Plan vs the normal health insurance.  On average,
in any given year, what are the percentage chances that anyone in a
family of 6 will be hospitalized?

Chances can be greatly reduced by food, exercise, stress reduction.

I would base it on the medical history of the individual as well the
ages of the people involved. Sometimes your car insurance covers a
component of this as well.