For this first one, I used transparency to blend the girls together as well, and added a gradient map to change the color a little. I also used Helen's vignette method - awesome tip!
For the second one, I kept both images at full opacity. I used image>adjustments>color match to make the man fit in with the rest of the picture. I also used a gradient map and painted directly on the photo to add some slight color in a few corners.