As others have noted, book the awards now as September isn't that far away & is still the "shoulder" season for vacations.

Your reservation will be for a standard room, which is the norm for award stays. Then call Marriott reservations & have them note in your reservation, "request upgrade if available". If you have any type of status, do "request Gold/Plat upgrade if available". That should (unless they're fully booked) get you to at least exec level for free & then you'd have access to the exec lounge.

The other thing (if you do have some flexibility) is when looking at dates, if at first they don't show up for award, pick "my dates are flexible" & it should show availability at the various properties/dates & you might be able to adjust a bit. Also, if most of the dates are available, but a single night isn't, have Marriott reservations call the property directly & ask them to open up inventory for the single night.

Since you're going to be in 3 separate properties not sure this will apply, but if you're thinking of staying at a property for 4-5 days, book a 5 day as the 5th night is free.

Hope that helps.

Cheers.