What very judgemental messages have been left on this thread.
There is no proof whatsoever that there are boundary issues in this family; why can't the father knock and then open the door to his daughter's room. The fact that people think there is something going on because of this makes me sick to be honest. It's more their disgusting minds thinking that something is amiss then anything else.
Going downstairs for a drink of water, regardless of time of day, or night, is a perfectly normal thing for anyone to do. I'm actually not sure why anyone would think twice about this. Obviously, if you live in a single storey house then going downstairs sounds really dodgy, but OP has established that there is an upstairs and a downstairs.
What on earth is amiss about a DD coming home at 1 am after work? She could work in a bar, pub, restaurant or similar or perhaps even in a care home. At least she has a job! I'm sure that if she didn't you would moan about that.
Leaving a handbag on the newel post is a normal activity. There is absolutely nothing wrong with that. Again, it's all in your mind and does not mean that OP lives in a disordered or chaotic house. Plenty of people leave their coats, jackets and bags hanging on gorgeous racks in the hallway - if they have the room!
What's wrong with pizza and a drink? For all you know, DD's room is really large and she has a retreat at one end, with couches and tables. As long as they take the rubbish away in the morning, it's all good, surely?
I am at a loss as to why DD was in the wrong for checking on her younger siblings. I don't see anything wrong with that and perhaps it's something she's been doing for a long time. It's good that DD is protective of her younger siblings and nice to see at a time when we are told that family values are not important to the younger generation.
The key in the back door lock? So what? It's not the be all and end all of life and if the person who left the phone did actually enter that way, there would surely be some evidence, as he would have to somehow get his hand in to the room to get the key, to unlock the door.
At a time when we, as women are seeing so much internalised misogyny in society, it's awful to see women tearing down other women and for what? There is absolutely no reason for all these comments. We should be uplifting our sisters, not belittling them, because they may well have other people to do that! Just a little something for you all to think about.