For light travel, I would "try" to go one camera + 2 lenses.
The trick is finding the right compromise of lenses; zoom range vs. size/weight.
Example1, for m4/3, my travel kit is 12-60 (my GP lens) + 17/1.8 (low light lens)
I selected the 17 on the logic that if it was low light, I was probably inside, where it was cramped, so a wide would be a better choice 'for me' than a normal or short tele.
Example2, for m4/3, for the primary travel lens, I use a 12-60 and my brother-in-law uses a 14-150.
I wanted a lighter/smaller lens than he, so I gave up on the long end.
Then there is the old 35mm PJ kit of 35 + 85/105.
So for APS-C it would be a 24 + 55/70, which would be your 23mm f2 + 56mm f1.2
Though if you want light, I would look at a slower 55mm lens, around f/2. This would be a compromise to reduce weight.
I have a 2nd set of larger/heavier lenses for use at home, where size/weight is not the constraint it is when traveling. And yes I have a duplication of lens ranges with the two sets of lenses, but since they serve different purposes, they don't really duplicate as much as one would think at first glance.
I like your idea of a smaller camera as a 2nd camera.
But, is there a smaller Fuji that has the same lens mount as the XT3? Then you can use the 18-55 on that camera.
I ask because, as with your XT3, sometimes my primary camera (Olympus EM1) is just too bulky to take with me, and I will take the smaller EM10 + pancake lens. The EM1 and EM10 share the same mount, so the lenses can be used on both cameras, and I can and do mix and match.