Keep middle kiddo RF for as long as possible & keep oldest harnessed for as long as possible....
In general, RF kids are safer outboard than FF kids & FF kids are safer in the center than behind a front seatback -- assuming proper installation according to both carseat + vehicle manuals (the safest place for a carseat is whichever backseat position allows for correct installation: less than 1" movement at the belt path)
I would choose a Sunshine Kids Radian for your oldest since it has the highest harness slots of all narrow seats. I would choose a Marathon for your middle child since it can tether RF & will puzzle nicely next to a Radian. The Chicco Keyfit or Graco Snugride are good infant seats, but you could skip the infant seat (carrying baby in sling) & choose a Radian since it fits newborns well (better than Britax + it tethers RF) or you could wait till baby outgrows the carrier carseat & choose a convertible later (maybe handing down the Radian if big kid is ready for a booster by then: in which I suggest the Parkway for 3 across situations).
Remember that the "best" carseat fits the child, fits the vehicle & is always used correctly! Each carseat must be
independently secure so I suggest visiting your local CPST for help....
Perhaps you'll be in the market for a minivan or larger SUV soon