Need help with 3 seats in 2014 Sienna

Hi all, we just bought a new Toyota Sienna 2014 on Friday and am already having problems with installation. We have a five year old that I'm trying to move into a booster and will have twins arriving this summer.
I had assumed I would put the 5 year old in his booster in the back row but when I went to get seats fitted at Buy Buy baby, they could not get any booster to fit anywhere other than the middle, which makes it impossible for him to buckle himself in as the buckle is so deep down the side. This was due to the headrests tilting too far forward to get a good fit on the sides of the seat, and I cannot see how to remove the headrests or tilt them out of the way. I have however seen photos online of people with high backed booster seats installed on the sides so not sure if they are just fudging it?
We also tried a 3in1 so he can maybe harness himself in rather than trying to wrangle the seatbelt, but it was HUGE and takes up almost all of the third row, leaving no room for anyone other than a child to sit next to him - who wold also prob need a carseat! I also don't feel confident he can get himself into the 5 point harness correctly.
Also, with the two infant seats installed in the captains chairs in the second row, I lose most of my access to slide the seats up to help him with buckling (I feel he's going to need help for quite some time). I can put the '8th' seat in the second row and attempt to put them all in a row I guess, but that defeats the whole purpose of the minivan as then we would never be able to access the third row at all. I am almost 6 foot and really cannot cram myself down the center 'aisle' to help him, I just don't fit. Other than going through the back lift gate to help him, I can't think of what else to do. And that would involve leaving a seat down and losing seating or storage space as well. Argh!

I hope this all makes sense. I am hormonal and nearly cried the other night when we were trying to get his booster. I'm not a huge fan of the minivan but thought it was necessary to fit them all and now I can't even get the seats to fit the way I want! Any help or suggestions at all would be greatly appreciated. Many thanks

I hope someone with more Sienna experience can jump in with more details on getting a good outboard install in the 3rd row, but have you considered removing one of the captain's chairs? That would give you much better access to the 3rd row.

The consensus around here is that the 2011 Siennas and later are not particularly car seat friendly aside from the captain's chairs. (I know, I just suggested removing one of them...)

Thanks but that wouldn't help me as then I wouldn't have a place to seat the second infant

Just to clarify, we will have two newborns and one in a booster. I can barely fit the one booster in the 3rd row, much less a booster and a newborn. I feel I must be doing something really wrong, as I have seen photos online of people with like 3 car seats in each row. But never with an explanation of what seats they are using or how they did it.

Are there any threads on here that deal with specific car models? I appreciate the reply though

I'm assuming there's SOME seat out there that will work for your older kid outboard 3rd row. (Anyone?) then you should be able to get 1 infant in the remaining captain's chair and another in the 3rd row.

Alternatively, put the older kid in the captain's chair and the babies in the 3rd row.

yes, I'm hoping to get more replies here. I def don't want to take out a captain's chair. Honestly I would return the car before doing that. I also don't want infants all the way in the back. It just seems crazy to me that we can't find a booster that will fit in the third row

Hi! I drive a 2013 Sienna so same style. I have had no problems putting a booster outboard in the 3rd row. Some boosters however, don't play as nicely as others.

Can you possibly post a picture of the headrests you have in your third row? That is what is stumping me. The headrests in my van are very flat and can be used with high back boosters quite easily, but I also think this might be dependent on the exact model of seat.

The best place I have found for the booster is the passenger rear (the smaller side of the 3rd row split) and my 7 year old with motor issues can easily buckle when he is in that position vs the center or driver's side.

Thank you so much! I just saw this reply. I will take a pic and post later. Can I ask what type of seat you use?

The high back booster that I most frequently use in the third row is a parkway. I have also used the turbo booster back there.

I have installed a Parkway SG for my son in my friends 2014 Sienna outboard passenger side without any fit issues due to the headrest. My friend has 2 rearfacers in the captains seats and has one slid back slightly to allow more access to the 3rd row.

thanks so much