There is a Misconception that LATCH Car Seat installs are safer then Seat Belt Car Seat Installs.
It is typically easier to Properly Install car seat with the LATCH Attachments, however, there is a 65lb weight limit on the LATCH system. (Includes Seat + Child)
It is typically more difficult to Properly Install a car seat using the seatbelt, however since seatbelts are designed to restrain Adults, there is no weight limit, like the LATCH does.
So, a properly installed car seat using the Seat Belt can be as safe, if not safer, then a LATCH Install. Also, keep in mind that 4 of 5 of all car seats are installed improperly!
I would not put a Convertible Car Seat (Or any Car Seat that has a Top Tether) in the 3rd row, as there is no Upper Tether point to attach to. However most Convertables should would fit forward facing, with a Seat Belt Install.
I have a Chicco Keyfit 30 Infant seat installed in my 3rd row, installed rear-facing. As far as Infant Seats go, that is probley the only Infant Seat you could fit back there, as it barley fits. My Grayco Snugride 35 won't fit back there.
I have a 3.5 year old, and Twin 1.5 Year Olds. I have a Convertible Forward Facing seat in the 2nd Row, and a Rear Facing Infant Seat in the 2nd Row, and another in the 3rd row. This works ok for my current situation, however once the twins are old enough to go Forward Facing, or they outgrow the Infant Seats, I will be switching over to the Dino Radian RXT, so I can fit all 3 across the 2nd row, which will be the safest bet.