Get
Virtual Audio Cable.
Set up a virtual line 1 (should have one by default with normal VAC install).
Set up a virtual cable that goes from Line 1 to Speakers so that speakers hear what is coming into Line 1.
Set Line 1 as your default playback device.
Set Skype to use Speakers as your default output device.
Optional: Set OBS desktop audio to use Line 1.
Note that there is not a good free way to do this.