DS1's Regent is expiring next month so I'm getting ready to play the carseat shuffle.
In my car I will get rid of the Regent and move his Frontier (harnessed) in (currently that one is in dh's car). DS2 is currently in a Keyfit in the middle. DS1 is behind passenger seat.
In DH's car DS2 is in Keyfit in middle. We have a Nautilus (booster mode) and a Turbobooster as options for DS1. I hate the idea of ds being in a booster, but I'm out of options. He's 8 1/2 years old and plenty big enough.
So do I move ds1 to the middle in dh's car and put the baby behind the driver? Or should the baby stay in the middle and ds1 (in the booster) stay behind the passenger?
We are thinking of getting a Symphony 65 for dh's car for the baby and a Radian RXT for my car for the baby.
There is absolutely zero reason (unless there is a special need you didn't mention?) that you should be concerned about an 8 year old in a booster. There's no evidence at this juncture that the harness is safer. For a child 5-6, a booster is perfectly safe. :-)
Ideally, the least protected child goes in the most protected position. In this case, that's the forward facing child. The rear facing child is the more protected child and therefore goes outboard.
In reality, it can be very difficult if not impossible to buckle a booster next to another restraint. Not enough room to get the hands in between the seats. Putting them both outboard is absolutely fine.
I'd suggest avoiding the Symphony. It's a rather short seat, outgrown early over all in every direction.
You want a seat that doesn't take up much back to front room. The Maxi Cosi Pria 70 might be a good choice :-) Or a second Radian with angle adjuster. More cheaply, Graco My Ride 65 and Evenflo Triumph 65.