Before I start, I'll note that I'm not a tech, but I'm pretty confident in my installs and have checked a number of things here via pictures.
Yes, tight would be an appropriate word. I question if I have come up with the most compact not-all-Radians puzzle ever, lol.
In the third row, my 3-acrosses are pretty limited; I have done (driver to passenger) RF Radian, RF MR, RF Coccoro; Radian/MR/Monterey, and I also accomplished Radian/Coccoro/Monterey this past week. If you have an older child, who is legal to sit without a booster, they certainly may pass the 5-step test without one back there, as well, which would help. I watch a 52" 90lb 8yo who passes five step, but he won't stay in position, so we use a booster for him. His 48" 65lb 6yo brother *almost* passes (I would not allow him to ride without a booster regardless, but just for sake of how those belts are back there.)
My typical setup is the Radian/MR/Coccoro, all RF, and I load them through the hatch. I NEVER thought that would be the setup that would work, but it's actually amazingly perfect. We don't have to fold the second row down at all to access the third row; the kids hop up/get lifted into the trunk area, take their shoes off, and pop over the back of the seat. I keep the headrests off, so it's pretty low, and even my older RFers are totally comfy back there. I am able to lift my 1yos into their seats while standing on the ground (and I'm only 5'4",) but I do have to climb into the hatch to buckle.
I have to have the second row slid all the way up to get those seats back there, although the 40 part where the Coccoro is can be slid back a few clicks.
Photos (It appears my second row here is Nautilus/RF Scenera/Monterey FWIW):
Best comprehensive shot I can get --
And from the side, to illustrate front to back room --
The Radian is braced. I would say that putting the front seat up changes the seat angle 1-2* at absolute most, but I'm truly not sure if it's changing the angle or just "settling" it by pushing the seat up against it. At any rate, I'm comfortable with the bracing.
I have "illustrated" photos of how the puzzling and depths work
here and
here if you're interested.
Before I figured out my third row setup, I had a Nautilus back there (60 portion, it doesn't fit on the 40, or I should say it doesn't fit easily/well on the 40,) as well as the Monterey. I can tell you that a Turbo does NOT fit on the 40 part of the bench; you can't quite get the buckle buckled. The high rise works great there, the Monterey works fine, I've also tried an old school Parkway and FPSVB back there (in my 3-across actually) and they work fine.
The second row has had a lot more combinations in there. This past week alone, I did (d to p) Monterey/Nautilus/Turbo, Nautilus/EBig Kid/Turbo, Nautilus/Turbo/FF MR, and Monterey/Nautilus/Cosco High Rise. All of the above were highback. My typical setup is Mont/Naut/ and then either a Pronto or a RF or FF Scenera on the 40 part. I can switch the Monterey and Scenera without a problem, except that I can't RF the Scenera there and then have to choose between tethering the Scenera or Radian. With the Scenera on the passenger side, I have the Radian using the drivers' side second row tether, the Nautilus using the center tether, and can tether the Scenera FFing. (The child in the Scenera is a tiny 4yo, so she changes directions based on however I throw the seat in that day.)
When I first got the vehicle I believe my combination was Scenera (?), RF Radian, RF MR. I was able to take out whatever the drivers' seat was and put a baseless SR22 in there for someone, and the MR and Radian were *not* puzzling in that sceneraio. They were side by side and totally independent.
The high rise is a spare backless I cart around with me, so it's buckled in just for transportation purposes, but here are a few pics of my current second row setup:
From the side --
Buckling this Monterey is super fun
(Not really hard or painful, just a trick to be learned...)
A bit of an "aerial" shot of the High Rise. The side of the Nauti overhangs the split just a smidge, so I can't fold down that part of the seat, but you still have tons of room on the 40 side.
Be aware that with the third row in use, there is zilch in terms of cargo space. I have a Graco Stroller -- one of the singles that would come with the travel system -- and it doesn't fit back there. I need to get an umbrella, one of the nicer ones, but don't want to spend the cash since I primarily wear lol. I borrowed a friend's Chicco this past week (I think it was a Capri) and I had to balance it very carefully on top of the stack of jackets, etc that lives back there.
I think that's all of mine I have to share, I hope it gives you an idea of the room that you have in each row and what can be done with some very careful puzzling.
Without knowing what kids you have and what combo of seats you need, I would think your best bet would either be to put the TF RF in the 3rd row, along with another seat (not a Turbo, although another booster with a child that could buckle it would be ideal) on the 3rd row, and load them through the hatch, or the Regent and a booster, if the child can buckle themselves into the Regent, and also load them through the hatch. If you're not interested in loading through the hatch, you *might* be able to get a 3-across with FF Radian/RF Radian/booster in the back, and then put two seats in the second row, but I don't think you could fit two same-direction Radians on the 60 in the 3rd row.
Otherwise, without hatch loading, I would do as Lysandra suggested and put two seats (one of the wider seats and a Radian, maybe) in the 3rd row, and make sure you put a booster on the 40 part of the second row, to access the 3rd row that way.
I hope that wasn't information overload. I just went through trying to get a vehicle that would fit six seats in it, and there just wasn't a lot of info out there, so based on that experience I feel like more information is better than less information.
