I know there are a few suggestions about this issue. Here is mine.
Rotation Angle Indicator
This dyn finds the rotation angles of each instance of selected family type based on a selected standard one.
Watch how it works
1. Find a same horizontal(parallel to xy-plane) curve(line) from each of instances.
2. Convert them as vectors.
3. Normalize the vectors and convert them to points
4. Create Arcs using each of points with origin as a center point.
5. Query each angle of created arcs.
6. Find reverse rotation angle and convert them to the same direction angles.
(Sweep angles of arcs from above step can't be bigger than 180˚. So need other way to find reverse direction cases.)
7. Convert them to Radians.
8. Apply Radians to shared parameters of family instances.
You can download the dyn here as usual.