Car seat help

Hi everyone, I need advise. I have a 2019 GMC ACADIA SLT1. With the 3seats in 2row and 2seats in 3rd row 60/40 split bench. 7seats. I'm due with my 5th baby. I'm having a horrible time trying to figure out what seats to get.

My kids are

11yrs 115lbs 5'

11yrs 100lbs 5'2"

Clearly no kind of child seat.

3years 33lbs and over 3' Currently ff in a Graco 4ever dlx.

22months 24lbs and about 30"tall

rf in a Graco 4ever dlx I'd love to keep him rf until at least 3 he's tiny for his age.

My dilemma my 3yr old loves unbuckling his chest clip, and can unbuckle the seatbelt if that is the install method used. So I want to keep him in the second row. For safety concerns. But also I feel they are still so young I'm not comfortable with either of my toddlers in the 3rd row. My 11yr olds are not responsible enough to be in the 3rd row with the toddlers either. So that is not an option.

what seats will work 3 across in the 2nd row, still allowing the 40split to flip up to allow access to 3rd row for my 11yr olds?

Thank you.