Dad having issues what can be done, is this behavior normal?

First off I have no clue if my father is T1 or T2. Or T1.5(which I had no clue about) this post is more about what I have observed.

I also don't know if he has been diabetic his entire life or not but this all started about 5 years ago. What happened is that he became sick, he began to lose quite a bit of weight he is 6'3". He weighed about 250lbs. When he was hospitalized his weight was less than 200. For the 25 years I knew him he never had to watch his diet or do anything and never seemed to worry about glucose levels. Fast forward to him getting sick. My mother discovered him in a coma, when taken to the hospital I'm told "his levels were so high the machine could not give an accurate number" so I guess this statement is true or that's just how my family is trying to express to me his levels were higher than they should be. Long story short the doctors say he has entered into a diabetic coma. He was comatose for about a week.

Ever since this event he has had in my opinion crazy mood swings. He is no longer the care free person I knew growing up. He is very quick to anger. Keep in mind I do not live with them. I'm in the service and only visit every few years but I can see it that my sister and mother tip toe around him so as to try and not provoke an angry response.

My father's words are essentially that when he does become irrationally angry he can't control himself. He says that he can see and hear what he's doing but has no control over his speech or actions. I interpret this as he is an observer in his body but doesn't have control until a bit later. My mom tells me this happens when they can't get his glucose levels below 300.

I just left there home for this last visit and the entire week I visited his levels were never below 300. I'm told he is to take a pill which my mother explains as something that is supposed to make him urinate excess glucose. But this doesn't seem to be working. He seems to be actively trying to watch what he's consuming. I witnessed him checking his levels and using insulin. But it seemed ineffective.

My father says he feels like the sugar is "rotting his brain" when the levels are so high, I have no clue if he's just making a statement or if there is truth to this.

My sister and mother make excuses for his behavior because of his glucose levels but I honestly have no idea if his behavior is caused by the constant high levels of glucose or some other issue that may be aggravated by the glucose levels or maybe some other undiagnosed issue.

Another thing I myself witnessed was what appeared to be a hallucination. He said he heard my son tell him no and so he raised his voice at him. There were 5 other adults present and none heard my son say no. Granted it was loud in the restaurant but none heard it except my father. I still believe my son didn't back talk.

So I'm asking does high glucose for long periods of time cause brain damage, does it affect mood to make someone verbally/physically lash out, does it cause hallucinations.