As alluded to above, the step to 35" tires will require some expensive modifications that will not be necessary if you stay with 33" tires.
Perhaps the first question to answer for yourself is whether you need 35" tires or want them. Are your 33" tires the limiting factor in getting to where you want to go? Would 35" tires get you there any better?
There will be plenty of advice here on lifts, gears, steering, stronger axle shafts, better brakes, etc., and no shortage of suggestions on how to spend your money. However, if you don't really need 35" tires you can save a lot of money by sticking to the 33" tires you have, which can be put toward other modifications that make your family's jeeping experiences better.
To put things in perspective, there was a day when 31" tires were considered "big" and 33's were "huge." Now it seems that 35's are the new 33's and 31's are thought of as small.