can a member of a family sharing plan pay for their own purchases?

The inability to pay for ones own purchases, if you're not the organizer in the share plan, will this also be an issue for customers who want to take advantage of the new Apple TV features that have just been introduced to the public?

Yes the organiser has to pay for any missing balance.

Family members should buy and redeem iTunes gift card.

Until the gift cards are used up, the organiser credit will be charged.