Nozomi Shinkansen One-Way Family pass ;Tokyo to Osaka (Green-Reserved)

Hello- I need assistance regarding Nozomi Green One-Way voucher from Tokyo to Osaka. All that is available is the 7 days and 14 days passes and not sure how this applies toward my scheduled trip from Tokyo to Osaka on May 4th morning? I have a family of 4 including myself (2-adults, 2- children ages 8 and 10). I am from U.S.A., Hawaii and why I will be needing to purchase voucher to go to JR Railpass office to exchange for Shinkansen passes. Please assist me in purchasing one-way vouchers ahead of time for my scheduled trip on May 4th. Thank you!