There's a reason I put family office in "quotes", your view may be the Wikipedia definition of family office with $100M+ of investment assets, that isn't the view of many "family offices" out there and not matching Wikipedia doesn't make them wrong.

Second issue on valuation, logically you're totally correct. In a jointly owned family business logic and Excel aren't the only way the business gets evaluated. Depending on the structure a sale may even be blocked by a minority owner member so all parties have to agree it is a fair sale price to sell.

If this "family business" has built up $5-10M in investment assets and the operating business runs at a break even while the investments generate $1-3M a year in gains is it a small "family office" or a struggling family business with an excellent treasury team managing the investment assets?