I have very similar issues as you...minus the kids...but with 2 big dogs, the wife, and camping or wheelin' gear, I needed to solve this space problem without buying an xJ(I just love TJs', no offence). What I decided was that a roofrack was the way to go....I'm running 33" tires so I can get away with a lighter weight spare tire like a 33" x 9.5" on the roofrack and the jerry cans mounted on the tailgate. This set-up solves most access and weight issues. First off, it is unlikely that I will even need to get the spare tire down, as most flats can be repaired with a good plug kit. Secondly, the weight of 2 full jerry cans is no more than the weight of the stock spare tire acting on the tailgate. I built a nice tray to carry the cans on the tailgate on my last jeep, and on my new jeep, I just bolted up some can carriers from Modern made by Crown. The jeep isn't too top heavy with the pizza cutter tire on top. Idealy, I may go with a Garvin wilderness bumper/tire/can carrier down the road, but for now this set-up works really well.
RACKMAN