Thanks! It all worked fine in the end. The double easily fitted through the scanners and the buggies were gate checked at LHR, ORD and BNA. We had an issue for the final leg (ORD-LHR), as the gate agent told us we wouldn't get it back at the gate in London. But the crew was brilliant and put them in the wardrobe between CW and F. We also ended up with a bus gate at LHR so a crew member came with us to Immigration as we couldn't put the girls in the buggies whilst they were on the bus.

The Kids Zone of the BA lounge at T5B at LHR was excellent, as was the sound-proofed kids area of the AC at ORD (at time of travel the Flagship Lounge hadn’t reopened). BA crew were fabulous on both flights, keeping our meals back until the girls had eaten, offering help as and when, and keeping my glass topped up! Girls slept all the way home – we put them flat as soon as we were airborne and they didn’t stir until we got them up for breakfast.

Flying AA (YX on a 175) connecting to LY in a few days. I know that some airlines, when connecting, will give you the option for a "claim at gate" stroller to either claim it at the gate of your first flight to use during the connection or check it through on the connection and claim at the gate at your destination. 1) Does AA offer both options or only the first? 2) If they do allow claim at the gate of the second flight, any odds on whether that will end up working on the interline or whether it will just end up getting shoved into a container and only discovered when they unload at baggage claim?

In a recent flight with AA and a stroller on an E175.... I did a end of the jetway gate check, and the stroller was promptly brought back up when we deplaned. I reminded the FA before landing and she mentioned something to the gate crew on arrival. Worked out quite well.
I suppose I could have taken the stroller in cabin as a carry on, as it folds up smaller than a roll-a-board, but I didn't want to hassle with it then.

Not sure about LY policies, but most wide-bodies have a "bulk" cargo door where the can fit strollers, wheel chairs, and other oversized (read: non-containerized baggage) in.

https://www.elal.com/eng/family/infants has some info on strollers, about half way down.

I got yoyo 2 with the travel bag. You can put the stroller into the travel bag and count it as one carry one. Based on my experience, It works for almost all flights. I hope this help