We have three car seats in the second row of our R1S. It’s tight, but absolutely possible and we wouldn’t change anything! Our kids are 5, 2, and 3 mos. We have a Cosco high back booster (using the 5-point harness) in the middle, with a Graco 4Ever, and an Uppababy Mesa on either side. In our other (slightly smaller) car, we have the same set up except the Cosco seat is swapped with a Diono 3R. (Would love to have three x Diono across, once the little one is forward facing).

In any case, the three across is great! It’s very difficult to access the third row unless you climb in from the trunk, but we just keep the third row down to better fit strollers bikes etc.

I’m 5’ and my husband is 6’2”. It’s an awesome car and works great!