It depends on what configuration of carseats you're using in which direction. We regularly get 2 FF Marathons and a Parkway in the 3rd row of our Sienna.

Do you have one adult who could sit in the 3rd row with 2 carseats? If you have one convertible RF and one FF, it's absolutely manageable.

We usually get a Uplander for a rental, and there's room for an adult, a Marathon FF and a Parkway in the 3rd row.