Ok, y'all are clarifying my thinking here. Yes, the trolley sleeve is essential. Yes, the Appenzell looks good and sturdy so it's a really good suggestion. I wasn't sure if its size (18X13X6 1/2) works with United's 16X12X6. Maybe they don't check or maybe if we don't overstuff? And it doesn't look like it has a trolley sleeve. But you're right I needed to clarify that in my mind and now I can search for backpacks with trolley sleeves as the alternative. I'm just not sure a backpack is meant to hold that much weight, lol. Just don't know how it attaches to the carryon to make it easy to carry. The Veloce has a sleeve but doesn't look like it should be loaded that heavily. I was planning something slimmer like an Osprey daylite for the person as a day pack on our trip, so this personal item just needs to hold the blanket during the flight and doesn't need to multipurpose. In fact it can't multipurpose because then we'd be stuck and not packed up to move on.
Yes, I'm probably going to ask the doc for a letter as back-up just to prevent charges at the last minute if they balk. I've checked the three airlines and it none of them say the weight is total. ITA the one I was unsure about and I found a Reddit thread saying they didn't check any of the carryons anyway. At some point I just have to take the documents, do what I can, and go. Frankly, I'm not hopefully a letter would even mean much in Europe, based on some strange things I've ready online. I just figure we're not in the USA with ADA laws and should be prepared to rough it and not be shocked.
Ok so back to the Euroflight bag. It sounds like it works and I should go with it unless I find a sturdy backpack with a trolley sleeve that I like better. Oh duh, if the Appenzell works, that means any random school backpack I have lying around would work! I can test that out and see if it fits. Then I'll know what size backpack with trolley sleeve it would take. Or is there a way to attach a backpack without a sleeve? It's gonna be super top heavy at that point, whew.
You know, as I'm writing all this out, I'm wondering why I haven't looked at the RS spinner carryon. Really, when you get something that heavy on top, it's going to feel crazy and tip. The rolling carryon seems nice and durable and people have commented about the easy grab handles and jacket pocket making it better than the Ravenna. However the Ravenna might hold up the weight of that item better? Or it doesn't matter? I guess if you stop you just detach them, right? Then when you go to walk you reassemble? Usually we go through security (where I get pat downs, takes extra time) then we sit down to wait for our plane. Person sits with ipad while I get water, snacks, etc. Person sometimes waits with luggage outside a restroom. So I'm going to ask them about the backpack, but I suspect they'll want it with a trolley sleeve. The question is then whether that affects the choice of the carryon or it doesn't matter.
I've clearly lost my mind, lol. I'll go do the backpack test and report back. I'll try the backpack with the weighted blanket on top of some luggage we already have and see what happens. I'll be back. :)