We have a 2007 Liberty.... I don't have a
Radian to try out, but I don't think it would work anyway

I mean, I think it would install fine: just not 3 across

It's difficult enough in vehicles that have a hip width of 51-52"
What is each child's actual weight & height (with age)?
What are your current carseats?
Worse comes to worse, I have had 2 seats installed outboard in our Liberty + my 5 year old in a Ride Safer Travel Vest in the center
P.S. if you want to try the
Radian out just make sure the online retailer has a good return/exchange policy.