It may have to do with the overall exposure of each of the scenes taken. If you reverse the order of the scenes, does the first photo still look like it is overexposed and the last underexposed? If you can post an example, it may help diagnose.
I would agree with Mac that the Nikon PC NIKKOR 19mm f/4E ED Tilt-Shift lens should be a fabulous lens (I wish that I had one). However, I don't think that it is the most practical.
The possible advantages by using this lens are:
1) With that lens, you could use the Tilt feature for exterior photos of houses that were tall to eliminate the sides of the house (or any other vertical feature) near the edge of the frame from tilting inwards when the camera is not parallel to the ground.
2) You could also use the Shift feature to create a wider photo (after stitching in post processing) for both interiors and exteriors.
3) You may spend less time in post processing due to the prior advanteages.
The disadvantages are:
1) This lens is very expensive.
2) This is a very tricky lens to use. You can't just put it on your camera and start shooting as you must properly understand all of the adjustments. Perspective Control (PC) lenses are the most complicated lens to use for beginners. These do not act like any normal lens (unless all settings are at zero).
In addition, you can replicate both of the top two Advantages above in post processing if you have the proper skills. However, if you have the money and skills to use a PC lens then this is the one to buy as it will save you time in post processing.
I agree with Photocraig that you want to have a wide angle lens as you are often in tight quarters (e.g. bathrooms) and it also give you more room to crop in post processing. You do not need a particullarly fast lens as you will normally be using a narrow aperture to get more depth of field. I also agree that you need to learn how to expose for the daylight "view" through the windows and fill the interior with speedlights and reflectors. Getting the entire interior scene correctly exposed is critical and changing to a different lens will not correct this basic problem. If you have never shot interiors before, you are going to have to practice for some time in order to get the skills necessary to go into a house and expose properly.
I believe that it can also be done as a double exposure. I did something like this a few years ago. If I remember correctly, to mimick that shot you would shoot the couple outdoors pointing the camera up from a low vantage point into a very bright sky and set the exposure to create a silhouette of the couple. Now for your second shot, properly expose a shot into some trees. The trees will now show up in any area that is under exposed - as in the silhouette of the couple.