Buying JR Pass for Family

Hello!
I wanted to buy the JR pass for three people. When I do that through this site, would one of those people be able to activate and exchange the voucher in Japan earlier than the other two? They will be arriving in Japan two weeks before and intend to use it before the other two arrive.
Essentially asking if I buy three passes, do we receive three separate vouchers in the mail and can they be activated separately? Or is it all tied together on one reservation and have to be activated all together?
Thanks!