Oh, I see what you are saying now. When i searched frozen pelvis, I got alot of information on advanced endometriosis, when the bowels and organs in the pelvic region fuse together.
As a person who spent the majority of his youth playing video games and sitting in front of the pc, I actually feel ok in answering this question 
Since they have spent the majority of their life sitting down and not being active, step one should be getting them motivated enough to stay active. Step two would be starting them on basic fitness and flexibility. Chances are that they have poor motor skills, so any classic games I would assume would help with that.
Mike- would lifting help correct some of their posture? I would assume all that sitting leads to a weak core, and that even basic lifting would help straighten them out.
Any knowledgable voices have more stuff to add or rebuke from mine?