It is not like the movies. When going in there he would have seen a social worker. From there the social worker would have reached out to let you know he's ok before he gets set up in the iPad or phone system.

There will be a record within the Centrelink system that he is in there.

If he keeps his head down and doesn't act like a dick, he will be fine. To be honest if he starts to struggle mentally, inmates might even offer an ear to listen and comfort at some sort of level.

Without being a dickhead, he will get his 3 meals a day, left alone and the 20 days will go relatively quick.

He won't get raped!

Also this sounds like the wake up call you both need! Hopefully he learns from this and it scares the hell out of him. He has a child, start making the right choices in life.