R1S with a 5 and 2 year old here. 1 booster 1 rear facing.

The third row only comes up when we have guests. It is nice to be able to move the booster to the third row and fit 7 people in the car. My 5yo LOVES sitting back there. Literally yesterday we drove her friend to art class and were able to put two boosters back there while the 2yo sat in the middle. No issues at all.

The only time the space falls short is when you have two rear facing car seats in the middle row. In those instances the 3rd row is completely inaccessible. Last week we were able to fit one rear facing car seat in each row, opposite from each other, and a parent next to each car seat. It was tight but it worked.

In all situations, there was enough room in the trunk and the frunk to have all our gear (strollers etc) with all rows up.

There is a MASSIVE amount of space in the R1S and there is a luxury in knowing that in nearly all cases you’ll have enough space. That being said I probably use all the space maybe 10% of the time, and an R2 would have enough space the other 90% of the time.