With all due respect, this is a silly question. I could rephrase the question to say "How much income must you earn to support your family's travel plans?"
The answer is simple:
Q: How much do the travel plans cost? $X
A: Then, that's what you need to earn: $X
Obviously, flying in Coach (as I do) is cheaper than flying Business Class. So, if you have $X in income and cannot earn any more, you can buy more Coach tickets than you can Business Class tickets.
You can certainly maximize your FFMs by flying certain routes, mileage runs, credit card purchases, etc. There comes a point where you have maxed out your signup bonuses, your mileage runs, your own flying, your own spending, etc. Take that number, whatever it is, and see how your family's travel plans fit.