You could get two in there ok. I assume you'd want to leave them though, because otherwise I could see it being a pain to get them in and out. You'll have a bit of room in the back even with the seat up. It's not Suburban size, but it's roomier than my Tahoe was back there with the 3rd row.
I put my twins car seats back there on occasion when i need the second row for some adults. If you use a seat belt tensioner (the Gold colored double T looking thing) then they fit back there great. With the Captains chairs folded up its almost like riding in a limo. I have even put em back there without the tensioner but only for short distances when I did not want to screw with it. If you sit in the seat and pull the seat belt tight it will get pretty tight on the car seat but it still slightly jiggles. I wish they had put the Latch Points in the 3rd row..
Two carseats sit back there great. My 7 month rear facing seat and 3 year old front facing (huge) car seats fit back there fine. You do not need the tensioner in our cars. If you pull the seat belt all the way out, it will retract and lock. This is specific for car seats and a lot of newer cars have this. It is shown in our manual how to secure the car seats. I just love my Armada!!
Actually the third row does have an anchor point for the middle seat. It is back in the cargo area with a plastic cap over it. I don't believe however that there are anchor points for the front of the car seat (if that makes sense).