A few things you might not be thinking of:
1) Do you plan on carbonating these? Do you have bottling equipment to do so?
2) You realize that if you just ferment out those juices, the end product is NOT going to be sweet? They will be dry and maintain some of the fruit flavor, but won't be sweet. If you plan on carbonating these, the backsweetening procedure for bottled beverages is a pain, in my opinion. If you don't plan on carbonating, save about 10% of the sweet juice, then add it back to the fermented juice right before you put the beverage in the fridge. The cool temps will hybernate the yeast so they don't ferment those sugars.
3) If you have a homebrew shop near you, go pick up an airlock and a stopper for whatever you are fermenting in. It should cost you about $3.00 or so total. If you can't pick up an airlock, just cover the top of your fermentation vessel with about 3-4 layers of aluminum foil and poke about 10-15 holes in it with a paper clip. Not ideal, but about 95% effective, and much more practical than a balloon.
4) It will likely only take 2-3 days to fully ferment the juice at room temp, but go ahead and leave it for 2 weeks to be sure, since you won't be doing any hydrometer readings. Also, note that any of those juices are going to take a good 4-6 weeks to condition at room temp before they are really drinkable, and they won't fully mature/peak until more like 4-6 months.
I do alot of hard cider. Feel free to ask any questions you may have!