I was blown away the other day by a post discussing single buggies that can go in the overhead locker but I'd be amazed if there was a double that could. Do people not understand how restricted space on a plane is? Cabin baggage should be kept to a minimum and taking a double plus I bet a few bags, nappy bags etc to go with takes up quite a lot of room. Where are the people behind/in front/next to you supposed to put their things?
There’s no extra allowance, except for a nappy bag if you have a lap infant. So you choose if you’d rather a stroller, designed to fold to the airline approved size, or a carry on suitcase. No special treatment! If you’re late boarding and the locker is full you have to gate check.
The airlines are the ones actively encouraging us to take all this hand luggage and if you have a bee in your bonnet about locker space then I’d direct it where it belongs- at airline’s and their ridiculous luggage fees, not parents trying to make their lives easier.
Also not all airports do gate checking, they’re supposed to have loaner strollers but these are often hard to find or not newborn suitable. If you fly through one of these regularly (I do!), have had your luggage lost (also been there) or have had a pram damaged in the hold (hasn’t happened to me but it has to friends) then you’ll be really glad of having a carry on pram. The YoYo is hands down the best piece of baby equipment I’ve bought.
So OP- I’d go 2 YoYo’s with the connectors, or just push one each, unless your eldest could get away with the buggy board then I’d do that instead. Keep in mind though that usually only a passenger in a seat gets overhead allowance (and sometimes you even have to pay extra for that with certain low cost carriers). So keep that in mind when you’re deciding what comes on the plane with you.