2011 Toyota Sienna third row three across solution

[turtlemama]

I used to be a CPST. I know how to install and pick seats, but my third row is giving me issues and I am not sure what to try next. I have five kids in my vehicle for now.
Seats and kid stats are:
9 yo, 62 lbs, 53.5 inchest tall, Incognito or Harmony youth booster
7 yo, 52 lbs, 48-50 inches tall (I can't remember his exact height), Harmony youth booster
5 yo, 42 lbs, 41-43 inches tall, Recaro Performance booster
4 yo, 38 lbs, 38-40 inches tall, Britax Pinnacle 90
9 mo, 18 lbs, 29 inches tall, Britax Marathon 70 RF.

I have tried three across the center row using the Probooster, MA70, and Pinnacle, but it didn't work out. The MA70 came unbuckled when my son unbuckled his booster.
I tried the Pinnacle in the center third row with a lbb on each side, but they couldn't buckle.
I put the 5 yo and 7 yo in the third row and the other three in the second, but I can't reach over the second row to buckle the 5 yo. His booster is too wide for him to buckle himself.
My last idea was to put the 5 yo in an Evenflo Sureride on the passenger side third row to give easier access to the seat belt buckles for the booster riders, but that spot doesn't have a top tether anchor.
Before I buy the Sureride, I guess I need to know if it will fit in the center third row?
If not, I am open to suggestions on very budget friendly seats for the 5yo. Or if anyone knows what I can do with my current seats. Thanks!

 

[MommyShannon]

While it's a little trickier loading, try the MA70 RF in the 3rd row. The base makes buckling boosters much easier. In my Ody I can put it and 2 Harmony youth boosters or Harmony and incognito and everyone can buckle. The MA kind of fits over the armrest bump on the side. Load the baby through the hatch or have an older child load and then buckle through the back.

 

[turtlemama]

I'm going to try that and see how it works out for a couple days. Thanks.