I believe it would depend on the kids size--3 car seats? 3 small youths? tight is the word that comes to mind...rode to Vegas in the rear seat with an Offensive Lineman from UCLA (300+lbs)in what I think was an 92 Jeep. Not terrible cramped but not exactly roomy either.
That's nothing. March, 1969, we are moving from Portland, OR to North of Seattle, and it was Mom, Dad and five children, ages 4 through 13...four boys and one girl. We all went in a 1966 Volkswagen type 1 convertible: Mom and Dad in the front seats, I was on Mom's lap, Jeff was in the cubbyhole behind the rear seat, and Fred & Tim sat on each side of Liz in the back seat. She didn't shut up the whole way up.
I owned a Wrangler once, but it didn't have a backseat so I have no idea if it should have 3 belts or not.
After belts comes age/weight of the little ones, do they require car seats?
CO recently changed their carseat laws (without really informing the public), we're one baby step - pun intended- away from a full 5 point safety harness for kids. You may want to research your State's carseat laws.
Easily done. I grew up in the back of a wrangler, many cross country trips while loaded up with potted plants, clothes, snacks, boxes, and two parakeets.
It's tight, but to be honest it's tight for ONE kid alone if he has normally long legs.