2011 Sienna 3rd row help!

I have a 2011 Sienna, and really need help with 3rd row carseats.

This is the kid situation:
9 yr old: 66 lbs
7 yr old: 43 lbs (tiny)
4 yr old: 43 lbs
2 yr old: 27 lbs
newborn in a few weeks

Right now I have my 9 yr old in a Britax Parkway SGL on the passenger side of the 3rd row, and my 7 year old (43 lbs) in a radian latched in with the middle latches in the back row, which are kind of off center.
I have my 2 youngest in the captain chairs (i have the 8 seater but i leave the extra seat in the trunk, it's easier for the kids to get in without it).
Right now, I have my 4 year old in a Marathon, and my 2 year old in a Roundabout. Those two seats are expiring, so I need new ones. What I would like to do is put both my 4 year old and 7 year old in Britax Pioneer 90's. In the back row. With the Parkway. I can't try it because I live overseas, so I need to bring the carseats back with me on my next trip to America. So anyone know if there is any chance this will work? I REALLY want to put all 3 in the back row. Another option is the Parkway, Radian 65 (which will expire in 2 years), and Pioneer 90.

Any advice?
Thank you!

are all of them Forward Facing?

I highly doubt 2 pioneers and a parkway will work back there they are just so wide and won't puzzle with each other. Pioneer rf radian parkway might fit.

You can fit a parkway, pioneer, and a radian. Not 2 pioneers.

Also-the Pioneer is a 70# seat with 18" harness the frontier is the 90# with 20" top harness and click tight.


I'd hate for you to get the wrong one and not be able to fix it from overseas!

If you only have 1 tether in the 3rd row, you need to put 1 rearfacer, a booster, and a forward facer in the spot with a top tether.

OP here- i totally made a mistake. i want to put 2 frontier 90's and a parkway. all forward facing. the youngest is 4 1/2 and 43 lbs, so no rf for him. i will have to install with seat belts, the latch is off center. i doubt i will have room for this.
maybe a parkway, frontier and ff radian. then in another year i will buy a parkway for my seven year old (she's tiny but seems to be growing, we took her to the doctor yesterday). would a parkway, frontier and ff radian fit?
would 2 parkways and a frontier fit?
thanks!

I have a 2013 Sienna (same model) and the same seats in question. So...

On the passenger side, put the booster. That will give the booster rider buckling room. Then, do the Frontier then the Radian. Is tethering every seat ideal? Absolutely. Is it always going to work? Unfortunately no. I would tether the Frontier and leave the radian untethered because of testing from Candada we know it does better than other seats untethered. It is a bit tricky to get both the frontier and radian installed and you have to buckle and not tighten the seatbelt until both are actually buckled, but it is doable. You can not fit a booster next to a Frontier on the driver side and expect the rider to be able to buckle.