Please slow down and read the bits of the legislation I'm posting. Under the current definition of a flight that is 'cost-sharing' it is not necessary for each and every one of the POB to share the costs equally.
I say again:
That element of the definition is: "the pilot in command pays an amount of the direct costs of the flight that is at least equal to the amount that would be paid by each person if the direct costs were evenly divided between all persons on board".
Please read that twice.
You work out the direct costs (as defined), divide them by the number of POB, and to satisfy that element of the definition the pilot in command has pay at least that amount.
Example: The direct costs of a flight are $7,000 and there are 7 POB on board including a babe in arms. To satisfy the element of the definition, the PIC has to pay at least $7,000 [sorry: at least $1,000]. Full stop. It's irrelevant that the babe in arms pays nothing.