It all depends on the ASA, the T-Stop you're going to use, the size of the room and the size of the window.
However, if you are going to use, let's say, an Alexa rated at 800ASA with a Tstop of 2.8 in a normal size room you could use a Skypanel above the window.
I suggest the Skypanel because you can change the color on it (it has loads!), the intensity, it has different facets that you can use either to make it more direct or softer and it is small enough to fit within anything!
Alternatively you could use a M18 / 2.5K bounced off a 1.5 meters x 1 meter polyboard above the window on an angle and use scrims to reduce the intensity of the light if needed.
That's for the one on the side.
For the one behind if you're going to see it I suppose that if you have to black it out you could use venetian blinds almost closed and a bit of light coming from the exterior to not give away that the exterior is blacked out.
You can see an example of "moonlight" done with Skypanels with blacked out windows on the following commercial I shot last month.
Take into consideration that the commercial had to have a very bright look!
Shot on Alexa Mini at 800ASA with Leica Summicrons at T2 1/2.
Have a good day.