My warrior cat au changes ages and messes with the timeline a bit for a few reasons:
Humans don't age like cats do so either we get weirdly large timeline expansions or I condense plotlines and mess with ages a bit.
Sometimes it gives me the chance to make bad things worse.
Hollyleaf is the middle child, and Jayfeather is the oldest while lionblaze is the youngest because even though they're triplets, I still think you can get a certain level of angst from doing it this way.
Jay is the oldest and because of that, him not even having the chance to choose his path and feeling like a failure as the first son will be that much heavier. Oldest children are the responsible ones who protect the others. And everyone took a look at him and decided he couldn't, he had a preset destiny by starclan. In a way he still achieves his goal of being a caretaker to his siblings, but not in the way he wanted.
Holly being the middle child means when she disappears, that gap feels present. There is a space between lion and Jay that should be filled but isn't. She's often overlooked and even when it comes to the prophecy, she was forgotten by those who initially seemed to promise her importance. Her brothers are awe-inspiring, her entire family achieves such wondrous things. But she always feels left behind.
Lion is impulsive, he's not dumb but sometimes with how he acts that can be easy to overlook. He's not the first son so he doesn't really carry the same weight Jay does when it comes to expectations. But even still he knows the family he's from and as such that weight still exists. As the youngest the other two always had an eye on him. He still maintains a role of being a concerned sibling who locks in when it matters.