The only family advantage:
if you employ a family member, the island pays for some of the salery. the amount depends on what the island owner specified in the settings
also good because they can help you transfer and u them ect its often used because u like the person and u get to know them and are friends.
also used for business purposes like trying to achieve royalty and you can be business partners and have the same prices so that you dont have to undercut each other ect... althought obviously u dont have to be in a family to do that but yer.... ignore me!