Hello,
@mammaju, and a very warm welcome to Talking Point. I am sorry to hear about your dad and that you have needed to find your way here, but hope you will find Talking Point to be both supportive and helpful.
We all need support, so no worries there. This is a difficult and dreadful disease and while it's of course very hard on the person with dementia, it is also stressful for the family and carers. Definitely don't be shy to ask for help and never turn down any offers of assistance!
The delusions (the false, fixed beliefs such as "this isn't my house") are part of the disease and they can be very difficult to deal with. Generally, contradicting or reasoning with the person with dementia doesn't work well and may provoke anxiety, upset, or even aggression, so you may want to consider not reasoning with him. It was a hard learning curve for me when my mother was diagnosed as I didn't really know anything about dementia and had a vague idea it was to do with memory loss. I had no idea that while memory can be impaired, other things like executive function and planning and logical thought get impacted as well. I was told by someone earlier on, not to try to reason with my mother, as her "reasoner was broken." It is hard to wrap our normal brains around the brain damage that this disease causes, especially when the person is still talking and walking and looking like themselves. A broken leg is easy to understand but a broken brain, not so much.
At any rate, you might try reassuring him when he is upset. A lot of sympathy and empathy and reassurance in general terms that it will be okay, or you will take care of it, or you will look into that for him, and then try distracting and redirecting him. My mother is easily distracted with food (cup of tea, a biscuit, cake, chocolate, ice cream) but others might be distracted by a walk, or going to sit in the garden, or watching a favourite show, or listening to some music, or an activity of some sort.
There is some good information about communication techniques to try if that might be of interest?
The Alzheimer's Society has a lot of good information on their website and that may also be helpful.
I am not sure what sort of help and support your parents have at the moment but I wonder if there are any carers groups in their area, a day centre he might attend, that sort of thing?
I hope you will find Talking Point helpful and keep posting and reading here. Remember, it's always open so you can stop in any time!
Very best wishes to you and your family.