Question Three carseats in third row of Nissan Quest

I have twin 5 year olds (one is over 40 lbs, the other isn't) and a baby on the way. I also have a Nissan Quest 2013. I would like to install all three car seats in the last row, so that I can fold down the captains chairs and have the extra space. The problem is that the third row seat behind the driver does not have an anchor for top tether, and the Nissan website says "Do not install any CRS requiring the use of a top tether in the driver side outboard seating position". My original plan was to put the baby in the middle and my twins on the outside, but I have Britax Marathon seats for the twins and Britax says "You MUST always use the Versa-Tether when using the child seat forward-facing." We do have a Diono Radian in my husband's car, and they say "If vehicle does not have tether anchorage points, consult vehicle owner’s manual or contact vehicle manufacturer with questions. " and "Stability of installation can be improved by using top tether " Does this mean the seat can be used without the top tether?

So here are my questions:
1) Can the Diono Radian be used without a top tether?
2) Is it safer to use a 5 point harness seat (Britax or Diono) without a top tether than to use a booster seat? (I know that 5 point harness is better with the tether)
3) Do I just have to give up and only put two in the back and put one in the captains seat?
4) Is there some other option that I am not thinking of that might work?

Thanks for your help!

Are you in Canada? Or California In Canada tethering is legally required on all forward facing child restraints. In the US, it is highly recommended. I would rearrange them such that you have two in the 3rd row and one in the second, and you will still be able to put down one capt chair for extra space.

Edited to add, kudos to you for reading all of the manuals and asking all of these important questions!

The other option is to put the twins center and passenger side and the baby driver side. The 3rd row is very narrow, though. I haven't been able to find information about successful 3 across in the forums, but the Quest isn't super popular, so there are pretty limited questions about it. It's probably possible to do, and that Radian may be a good start.

What do you want the 2nd row space for? We might be able to brainstorm alternatives for that need.

Thanks for your responses. California, not Canada. Yes, I have thought of these options, just trying to see if there is a solution I haven't thought of.

Nothing specific at this time for the space, just trying to make best use of the space available. Probably things like bringing bikes to the park and other stuff that I have been able to do with the back row folded down and my kiddos in the captains chairs. Having room for a shopping trip to Costco and having a stroller in the car. I have used the space in the back of the minivan so many times just for random stuff, and so just trying to figure out a way to still fit big bulky items when I need car seats in the third row.

The problem with using the space in front of the kids for storage is that anything stored there will be a projectile in a crash, projectiles are extremely dangerous and can often be lethal. Anything in the passenger compartment should be secured so it can't kill or injure.