Here is a scheme of your problem. The axis are in black.
The Qs are the red dot. The qs are the green dot.
The force Q on Q is represented by the red arrow.
The force of the qs on Q are represented by the green arrows.
Their projection on each axis is represented by the yellow and blue arrows.
You can see that the yellow arrow cancel each other.
Two superposed blue arrows have to compensate for the long red arrow.
The blue arrow have of the magnitude of the green arrows that represente the full force of the qs on Q.