Hi there,
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Yes, keeping your 2yr old rear facing (RF) is the best way to go. New recommendations state 2 as the bare minimum to turn children around, and staying rear facing until the maximum rear facing height and weight allowed by the seat is considered best practice. The Radian will allow many children to rear face to 4 years old. If front-to-back real estate in the car is at a premium, there is an angle adjuster you can use to have your 2yr old's Radian more upright, and allow more room for the front.
So just to clarify, you are installing one Radian RF, one Radian forward facing (FF), and one Graco infant seat? Do you know if the Graco is a snugride 32, 35 or ?? They do have slightly different shell structures.
One general tip to fit 3 across is to install all seats using seat belt instead of using UAS. Using seat belt enables you to push the outboard seats a little further toward the doors to give you a bit more space in the centre.
Also, the seat portion of the Radian is narrower than the shoulder portion so usually, puzzling a FFing and RFing next to each other is usually easier than putting two side by side that are facing the same direction.