I'm going to take a backseat on my group project
What makes you want to take a backseat on a project?
I want to take advantage of this situation for my private purposes.
This is a group project, so you are expected to do your fair share of the work. Your group members may not take too kindly of your laziness and decide to speak badly of you.
I don't care, they can do it all by themselves.
I wouldn't expect to get away with this, as they could tell your teacher and you won't get credit. Discuss dividing up the tasks and stick to what you are good at, so you can contribute.