1 is probably wrong since it would mean that they are always on the same hemisphere, which is rather unprobable.
Lets look from this point: The first fly lands on the orange. It doesn't really matter on which half. Now the second fly has two different possibilities. Either she lands on the same side or not.
Therefore the probability is 0.5
Alternatively write down all possibilities (should be 4) and those that suit (should be 2) 2/4 = 0.5