I’m not saying it’s needed in the Y, but for less wide seats we used CLEK (foonf?) in the 3 and fit three side by side.
They also have some nice convertible boosters with backs that also click into LATCH
Yes the car seats do fit, problem is the kids feet don't reach down under the middle row seat. Their feet will be all twisted up and uncomfortable.
It's a tight fit in my model X for my son back there when he is wearing winter boots. He has his feet pointed to the side. I don't see how it would be any more comfortable in a smaller car.