It can work but you really need to focus on overlapping times within your return window and by not trying to match the start times to your exact return window start.
Yes you can book for all guests that have the same resort stay start time at the 7 day mark.
They don't even need to be at your resort. But you need to confirm that you have everyone linked in your Friends and Family list and that you are sharing plans with everyone that has a
MDE account (they may manage additional members under their MDE account).
Is it possible that you could share the LLMP and/or LLSP initial scheduling with another MDE account holder? That would make your booking day a little easier as you could book for the first group of your travel party and alternate days or divide your park days and have one person do the first part and another focus on the second part and book at the same time.
For the group that arrives at a later date you would do the same process again but it will take a little longer as you spend your 5 minute window that LLMP selections are held to try to get any overlap possible. If you have 2 people working on this it should make it easier for each of you to focus on overlaps on a per day basis.
Does this make sense?
Dave