The most "Touching up" of photos I have ever attempted is with old (pre 1060's) black and white photos which have become spoilyt over time. I have airbrushed 'faults' in the photos before loading them on my hard drive; by that I mean "correcting areas of age realated physical damage", but nothing much more.
I wanted to take on such a task with the following two pic, and I would be fascinated to see what you could achieve. The first is a photo of my older son and his Girlfriend.
The second is one of my Wife, my younger son, and me at his Graduation (which his older brother could not attend, because of work). I wanted to try and "add" my older son to the second image; I would be interested to see what you can do..........
( had thought of trying to add Andrew to either between us, or to one side)
Picure 1 (I have kept the quality high to help you)
Picture 2 (The graduation) - to which I wanted to include Andrew:-