Question HELP! 3-across convertible in Mazda CX-9

Hi All,
Thank you for having such an awesome website and forum! I need your help and expertise please!

What seats can I buy to go with Britax B70 to fit 3-across in the second row?

DS (behind driver, LATCH)
2 yrs 6 mos
38 inches tall
36 lbs
currently RF in Britax Boulevard 70

Twins are each (middle seatbelt and behind passenger LATCH)
11 months
29 and 30 inches
23 lbs
currently in Chiccos

I have 3 boys, and my 11-month old twins are currently growing out of their seats. They are now in Chicco Keyfit 30s but are almost too long for the seat.

DS is a GIANT 2 year old so may need to turn FF soon as he is nearing height and weight limits to RF in BB 70. I want to keep all of them RF and 5 point harnessed as long as possible.

I am leaning toward Diono Radian RXTs because of narrow profile, high RF and height, and I like RXT because of side impact over regular Radian 100 or 120.

Concerns:

1. DH is 6', I am 5'9'' so concerned about fitting Radians RF.
(I know about angle adjuster, does it really help enough? I heard it smooshes down over time (like just a few months) and therefore stops working because the seat becomes more horizontally angled. Is this true?)

2. How should we configure the seats? Especially since my 2 year old is giant but not so hot in the motor skills dept- I'll have to have access to all 3 of them to buckle them in.

3. Wish we could just buy a minivan but that is so not happening. Please help if you can- thank you!

Hi!
With the angle adjuster, you might gain a few inches of space. It makes a huge difference. I don't think that the new angle adjuster will compress over time.

I don't have tips for buckling 3 RF, unfortunately.