I would suggest Adobe After Effects. You can create what is called a Mask by drawing lines around the objects you want to either remove or add from/to the scene. You can apply other effects to blend it in as well. After Effects works with layers so you can put stuff on top of other stuff in any order and duplicate layers and so much more. You can get a 30 day trial I believe when you first install it. Watch youtube videos on how to work with masks in after effects.
Good luck!