1- Between the two the Rubicon is not much "harder" to get into, most jeep owners get grab handles to help get them and passengers up and in for all models of wranglers. The rubicons come with standard grab handles built into the A-piller to help get in... Overall, not a big difference between the two. Side rails are easy to get on and off, few bolts on each side thats it, pretty easy to do at home with basic hand tools.
2- Not a huge fan of full-time 4wd due to the choppiness of a tight turn with it, but mpg wouldn't be too noticeably different, considering all wranglers aren't bought for their "amazing" mpg ratings. For off-roading there's a big difference between the two models, but all wranglers are built to handle off roading requirements, you can do a lot of off-roading in both models but if you want to do anything thats more than "light off roading" which is some light trails and rocks and such without making a lot of upgrades the rubicon is the "king" allowing for higher fenders and wheels in its stock form and comes with lockers for more serious off roading situations.
3-Depends on the tire, but the HA edition stock tires are defiantly a more pleasant drive on the high way and at speed, but with the stock wrangler setup it really isn't bad at all, even at speed. Rubicon may be a bit louder due to the tire size being a bit bigger and tire tread being more aggressive.
4- I have not removed any of the decals, but with a cheap goo-gone or 3M adhesive remover I'm sure it would not be a problem at all to remove whatever you want easily.
5- Just faced this decision 2 weeks ago... parents are buying me and my twin sister brand new from factory jeeps of any model we wanted as a grad present and I chose the white rubicon and my sister chose the white high altitude. Both 3.6 v6 because I am not a fan of the 2.0 Turbo and I heard they may even faze out that engine due to it being more problematic. I chose the rubicon because I really liked the look and the bigger stock ride height and money was not an issue. My sister liked the look of the sleek almost G-wagon look of the high altitude more. She plans on getting a cheap $250 small 1.5"-2" spacer lift to bring the factory ride height up without sacrificing stock ride quality
P.S.
In my opinion whatever Jeep you get your family will love.