Since DH had a 2001 Jeep Wrangler AND a Radian, I thought I would chime in. Since the backseat of the Wrangler only has two seating positions, both outboard, you're gonna have one Radian behind the driver's seat and one behind the passenger seat.
I have pics of RF Radian behind the passenger seat. It was very easy to install, but it does take up alot of room. Instead of moving the passenger seat forward (where my knees would eat the dash), I decided to make the front passenger seatback more upright, so I was sitting almost at a 90 degree angle.
I'd be hesitant to put a RF Radian behind the driver's seat, just because I think you'd have to move the driver's seat too far forward or make the seatback too upright for the driver to be comfortable.
IF was in your situation, I'd put your 4yo FF behind the driver's seat, and the 2yo RF behind the passenger seat. And since your son #2 is 2yo, you should try to keep him RF, but I wouldn't feel too guilty if you end up needing to put him FF as well, if you find RF takes up too much room.
Don't forget that Jeeps have roll bars, which...while not side curtain airbags, they do keep the frame of the Jeep from collapsing in a rollover.
Here's a pic of RF Radian behind passenger seat: