"Philip, we're leaning towards the Highland Trail. Trail info for the Western Uplands indicates a flood-prone area (April specifically) right by the trailhead, and says 'be prepared to wade'."
Yup it can get super flooded in this area if you hit the right conditions. I hiked this trail in April 2008. That year there was a lot of snowpack and then we hit 4 days of pure sun and day time highs from 25-28 C. According the warden, the four of us were the first four people around that loop that year without snowshoes. Roughly 75% of the ground was snow covered and we spent a lot of time walking knee deep in snow but with our shirts off because it was so hot.
When we started the Highland trail there was maybe of foot of water after the bridge, but after 4 days of hot temperatures we had to walk through several hundred feet of 2-3 feet deep water to get out.
Here's the flooding on the way in, and then on the way out. In both pics you can see the bridge in the background. The flooding gets better after 100-200 feet.
And another random pic:
To answer your questions, I would play things pretty safe with the gear for your wife but personally I would take just the NeoAir for myself. The R-value of the NeoAir is basically the same as the Ridgerest, so I see no reason to take the less comfy Ridgerest instead. You could bring both, but that's likely overkill. Especially if you camp in south facing areas that are less likely to have snow cover and should have somewhat warmer ground.