Can an individual in family sharing chose to purchase an item on their own?
Can an individual in your family sharing group purchase their own items and pay for them on their own?
iPhone 4
If they have a balance on their account then yes, that will automatically be used for their purchases - members cannot use their own credit/debit card (the organiser's card will be charged if the member doesn't have a balance), and the family organiser cannot use their own balance (only their card)