First that I've seen this done! Amazing you can fit all that in there -- how much foot/leg space do the kids in the 3rd row end up having? Pics would be super informative
I don't have 4 like you do, but there is a good chance that one of mine could see some forward facing convertible car seat time in the third row when family visits.
edit: I tried at an SC to put our Nuna Rava seat in the third row forward facing while other were checking out the car, so didn't get to do a great assessment, but it seemed maybe the kid's feet might always be scraping the back of the third row.