A blueprint rotator object is not a quaternion, but a struct of roll, pitch and yaw.
What I meant with the offset vector was this: When I assume that the offset vector is gathered with every call of the construction script, it would change every frame when you rotate the cursor actor (like the rotation currently does). But then you would rotate a vector that was already rotated last frame, so you would have the same spinning result for the location of the actors. But this was not the case in your last gif, so I assumed that you gather the offset vectors differently than the “offset” rotation.