As others have stated .. its not quite as simple as you are thinking.. but there is a way around that is workable. If you cannot manage the process, then let their visas lapse and start new applications 18 months prior to your intended return to the US
1. Pay the GC fees and enter the US all together prior to the visa expiry date Use the address of a trusted family member/friend as your US address.. the CBP officer needs to enter this into the system when you enter.
2. get SSN, drivers licences etc as soon as you can
3. apply for reentry permits for all of them. Request they be sent to the US consulate in the country where you are living ( do this on the I131 form)
4 You can return immediately but they must wait in the US until they complete the biometrics process OR more likely are notified that biometrics already in the system are being reused. They do not need to live at the address given to the CBP. Have a fun vacation !! They can then leave the US
5 Once the reentry permit is approved, it holds their LPR status for 2 years from the approval date. If this isn't ling enough they will need to apply for it again .. they must renter the US before it expires and apply as before from within the US Stay until biometrics are completed again.