So sorry you are going through this OP, it's a proper shitshow isn't it.
Falls in the elderly can be catastrophic. My dad was never the same again after his. There can be a bit of a "chicken and egg" thing going on, in that it is possible a ministroke caused the fall and thus diminished his mental capacity, but it is also possible that he was deeply disorientated by finding himself in an unfamilar environment. In the case of your dad, the powerful drugs they're giving him will also be complicating things.Even a UTI at that age can cause delirium, so a kidney injury is also likely to be making things worse.
I wish I could have wrapped my dad in cotton wool and ensured he was cared for beautifully to the end of his life, but in reality things didn't really work out that way as care decisions had to be made quickly based on what was available at the time. My only consolation is that he was confused enough not to really understand the position he was in, although I'll never really know.
The thing about food and liquid intake with dementia of any kind is that the area of the brain that controls appetite no longer operates as it normally does. There also comes a point where fluid intake is not properly absorbed by the body and just causes complications.
Things might get a bit messy from here on, I'm afraid. All I managed to do was visit him as often as I could (although that was exhausting for a million reasons) and tell him I loved him, and know that he understood. I wish it was different, I really do, and that I could give you more positive advice. Maybe someone else will. Good luck 💗