Popsicles are very easy to make at home, and regulating their hardness is very simple.
If the water content of the pop is too high, they end up extremely hard - like ice cubes.
Sugar and alcohol both help keep this from happening. By lowering the freezing point of the solution, they make the pop softer. Add too much, however, and the popsicle won't freeze solid enough to stay on the stick.
Once the pop is frozen it tastes much less sweet, so don't worry if the mix tastes too sweet before you freeze it.
Most fruits work pretty well with 1 pound puréed fruit, 3/4c simple syrup (boil one cup water and 1 cup sugar until clear). Watery fruits like melons benefit from more syrup, and very sweet fruits (especially canned ones) might need less (I use 2/3c syrup).
If you're going to add alcohol, use about 2 shots for 25 fluid ounces of mix. Any more, and the pop won't freeze correctly.
Pectin and gelatin also have an effect, but I find they give the finished pop a very strange texture - and they need sugar to set anyway.