2a. For this one i just took the plane and put 4 different size ones in one of the sky pictures.

2b.This is just a basic replacement of the sky.

2c. In this photo i first replaced the sky, then i changed the color of the shrubbery to purple, and last i put in the plane from the other photo and resized it to fit. I also threw in some smoke coming out of the plane and changed it to blue.