Hello everyone. As the title suggests, my wife and I are planning a round-the-world trip coming up in a couple months and we need new luggage. We are going to be traveling for 4+ months across Asia, SE Asia, Eastern and Western Europe, and Africa (Morocco, South Africa, and maybe Kenya). I currently have an Eagle Creek travel backpack that's about 10 years old now and my wife had a Osprey Farpoint 55, but we returned it. When planning for the trip, we decided we wanted to aim for one bag travel, or at least no check-ins. After a lot of research, we've settled on getting Tom Bihn bags. I looked at a ton of other options and was debating between a Tom Bihn and a Tortuga. If only Tom Bihn had a backpack with a waist strap to help distribute the load a little more, it would be the perfect bag. The bags are a little more than I initially wanted to spend, but the benefits seem to make it a worthwhile investment. Anyways, on to the point...

What we need:
-We are planning on packing light, but since we will be traveling between a variety of climates we will need a variety of clothes for cooler and warmer climates. No plans for extreme cold weather though.
-I will have a 15" Apple MBP, possibly may get substituted for an android 10" tablet with keyboard, netbook size.
-I also shoot with a DSLR, so will have my camera and 3 lenses total. I will need a day bag for this and have decided not to bring my camera bag to avoid drawing additional attention and to pack as minimal is possible.

Other than that, we are trying to pack fairly minimal. We don't have plans for anything fancy, so no addition dress attire. The only additional footwear we are planning is a pair of Vibrams since they pack small and so versatile for outdoor activities.

What I am thinking:
-For my Wife: An Aeronaut, plenty of space and versitle. Her day pack would be an REI Flash 18 that we already own. Packs small and carries plenty for a day pack.
-For myself, I was thinking a Tristar and a Synapse 19. I really like the Tristar design and it seems like the perfect weekend bag for future travels. My thoughts on the Synapse 19 is that a backpack would be nicer to lighten the load as my day pack with my DSLR. I was thinking of getting a minimal case for my camera in the main compartment, and then keeping my 2 lenses in a soft pouch in the side pockets.

Questions:
-Will the Synapse 19 fit a cache for a 15" MBP laptop? I was also debating between the Synapse 25.
-I've seen pictures of a Synapse 19 inside the bottom of an Aeronaut, but will the Synapse 25 fit in an Aeronaut? I dont think I would do this, but would the Synapse 19, empty, fit in a Tristar?
-Anyone have any other suggestions or combinations that I should consider?

Sorry for the long post and thanks in advance for any advise or suggestions.