The Attempt at a Solution
I've managed to do the first parts up till part (a) and part (b), where I have some questions:
2. how do you know where the E-field is zero? Is it in the region of space where there's some sort of special pattern?
I've found the PE of the system..
But for the last part, I'm tempted to say by the conservation of energy it shouldn't matter how you release them but I can't seem to prove it..