The Chevy Malibu doesn't quite have 3 full sets of LATCH. IIRC, recent Malibu models have those overlapping lower anchors that can be used for the center or outboard, but not 3 full sets. It's the Chevy Impala that has 3 full sets of LATCH that can be used to install up to 3 carseats with LATCH, although GM vehicles have a LATCH installation weight limit (child's weight) of 48 lbs. and seatbelt installations often are more likely to achieve a successful 3 across combination due to spacing of the seatbelt buckle stalks/seatbelt anchor points closer to the sides of the car relative to the spacing of lower LATCH anchors.
That said, 3 across is known to be workable in the Malibu, as well as the Impala, and in many other vehicles, given the right combination of carseats that puzzle together in the car. The forum's lengthy 3 across thread in the Carseat Chat section at
http://www.car-seat.org/showthread.php?t=33226 illustrates many cars and combinations of carseats that are workable.
ETA: One model to avoid that comes to mind is the Toyota RAV4 small SUV from approx. the 2006 or 2007 model year and newer. It has some overlapping seatbelt buckle stalks/lower anchors for the driver's side and center seating positions in the back seat that makes it very unfriendly if not impossible to install carseats side by side. It does have an optional third row available in 2006/2007 and newer versions, technically with third row seating for 2, but it's a very cramped third row and the third row also eats up most of the cargo room.