Yes, I’d take a simple assets minus liabilities approach.
Obviously, there are accepted practices for valuing businesses and professionals who do that for other purposes. But for the purpose of college FA, guidance is pretty slim. I’ve had a few conversations with college FA folks over the years and the answer was pretty much: what would you get if you sold the business today?
Check if you also need to do the CSS business supplement for any of these schools. I seem to recall a section on there for listing assets and liabilities.