I’ve gone through every light settings in the details panel, but found no fixes for the two other light sources. Source radius seems to be the only one affecting the edges of the shadows, albeit incredibly roughly and unreliably.
find the material responsible for shadows and lightning, play with the values and you will find the solution.
another solution could be to play with VideoCard Settings
another solution could be updating 3d drivers
UPDATE: Changing the Project’s settings Shadow Map Method from Virtual Shadow Maps to Shadow Maps has solved the issue for me. Shadow edges are now softer and have more realistic dispersing edges. Leaving this out in case someone comes across this issue.