yerrppp the point is to create a massive deficit so their body burns fat for energy, and with the ammount of fat these people have, they wont suffer because of this deficit for a long time.
however, if their body becomes accustomed the that much physical activity for an extended period of time, then it starts to need that in order to maintain let alone lose. they cant drop their calories any further, so what needs to happen? more exercise. but when your already doing multiple hours a day... its just completely unrealistic.
good luck to them, but they will hit a wall and it will be a rough gig getting over it.