I am so glad you decided to give me the exact schedule.
There are two time limits that come into play with Memory Maker.
The first time limit is that the photos themselves expire, and are removed from the server once they are 45 days old. This applies individually to each photo you have taken.
The second limit is the one I talked about before. Once you make your first download, you then have only 30 days to add more photos to the Memory Maker.
Now, with those two limits in place, let's see how this will work out for you (hint, I have a good feeling
Your first photos will be taken on July 3rd. Those photos will expire on August 17th. So, already, we know that you last photos will be taken on August 7th, which is 10 days before your first photos expire. That means that you could wait until sometime between August 7th, and August 17th and download everything at one time.
You could also download the photos from the first part of your trip before the second part of your trip. You need to add your last photos to the Memory Maker on August 7th. Counting backwards 30 days from there, we get July 8th. So, you could make your first download anytime AFTER July 8th, and you would still be able to add photos on August 7th.
I would either download the photos from the first part of the trip sometime in mid July, say after the 15th just to give yourself a little padding on the timing, or I would download everything as soon as your second trip is over, on August 8th or 9th. Either way, you will be well within your windows with no need to purchase anything else.
Enjoy your trips, and your photos