In other words you're saying that this place is just a really elaborate seal set up?

[No, no he's really really not a genjutsu specialist! Just. Family.

You would understand that part most likely.]

Like, one to revive people, one to keep them that way, another for transport ike Sensei's Hiraishin?

But how would they pick their targets? What about those whose bodies were seriously modified?

Sometimes people return to their 'normal' so the change isn't permanent...