Okay.
I'd put the 6 year old in the Prosport as far back as possible in the front, but I don't know if I'd put the 7 month old or the 5 year old behind that seat; it would depend on whether the 7 month old fit there with the seat all the way back (CA maybe, as upright as possible?) and which seating position gave teh 5 year old more head clearance (this would depend on driver's height too.) Even with a tether, remember that the 5 year old needs clearance too, and moving the front seat ALL the way back might not give the 5 year old as much clearance.
Oh, and if the RA50 would fit with the necessary configuration for the 7 month old, and the CA was lower-profile for the 6 year old, I'd use that instead of the ProSport to keep him/her further back.
If tethering to the center seatbelt or tether anchor wouldn't put the tether more than 20 degrees off, and didn't interfere with the seat behind the passenger seat, I might do it for the front seat, even though it's not an approved solution, I'm aware.
IF the airbag turned off WITH A SWITCH OR KEY I would put the rear-facer there instead, braced if possible, and the other 2 in back in tethered seats. But if it uses a sensor, no way.
