Boosters Age 10+

I have twins who are 10 years old and going into 5th grade. Neither passes the 5-step test in our main car, an older Honda Odyssey (and yes, they complain because here no one is in a booster past 2nd grade). Anyway, both kids are riding in Harmony Youth boosters, which we also use for travel and carpooling. Carpooling often involves 3-across. But my taller twin is 57 inches tall which technically is the height limit for the Harmony Youth. My shorter twin (bless her heart) is only 52 inches tall and will probably be in a booster until adulthood.

Do I keep the taller twin in the Harmony Youth or get her something like the Incognito? She's 75 pounds, 57 inches tall. We still need it to work for carpooling, 3-across, and be easy to travel with. Would it be bad to put the shorter twin in the Incognito as well? Shorter twin is 58 pounds, 52 inches tall, so not QUITE at the lower weight limit for the Incognito but it would also help her psyche to not still be in the "baby seat" while twin sister gets to move to a "less babylike seat". And yes, my twins are THAT different in size!!

What would you do and what are the recommended backless boosters these days? I'm already struggling because every parent involved in carpool wonders why they're "still" in boosters at all and to be honest, it doesn't matter how easy a booster is to use, it's still more of a pain when buckling belts (especially in 3-across situations where everyone's struggling to get belts tucked in the right place and buckled). But I am holding out as long as I can...

You can't use the Incognito yet for the smaller, but she can continue to use the Harmony. Your bigger can use it, though. And you can definitely get two, and have it on deck for the smaller to move into (remember, booster weights are fully clothed, in shoes. Everything a booster is expected to stop in a crash). Her height is fine, that doesn't concern me in the least. It's solely her weight.

Wendy