Yes, definitely at least call the doctor. Even if the answer is, “This is just a progression of the disease, sorry, but you’ll have to learn how to cope,” then at least the doctor knows that the disease is progressing, and has this new symptom to put in the file. When another symptom pops up in two months, it will be documented as a continuing progression, not look like two symptoms have popped up at the same time (which would probably trigger more invasive and aggressive testing than it really warranted.)
Acute confusion and belligerence is indeed part of the progression. But, as mentioned, it can also be a sign of a stroke, oxygen deprivation or an infection (commonly a Urinary Tract Infection) that would call for a change in treatment. Best person to figure out which it is would be the doctor. If he knows he took a urine culture two days ago and UTI is unlikely, then at least he can make that medical decision for you.
For in the moment advice, yes, keeping calm and trying to redirect his attention is about the best you can do. I find it’s sometimes helpful to agree to their demand with a delay. “Of course, we can go to the store this afternoon, after we eat lunch.” If you’re lucky and keep them busy in the meantime, they will often forget your “promise” by lunchtime.
Try playing some music from his teenaged years. I find that can help to put them in a better mood sometimes. I even had one lady who was in the late stages - she couldn’t really talk anymore - who came out of her fog when she heard a certain song, and danced with her husband and told him she loved him before slipping away again. They cherished those moments, as did I. Music is powerful.
While there is not yet scientific evidence to support it (a placebo controlled trial is in the work as we speak, but the results are not expected until the end of the year), I have read some interesting and promising case studies on the addition of coconut oil to the diet of those with dementia. I would NOT recommend stopping any medications or scientifically proven treatments in favor of coconut oil, but you might want to talk to his doctor about supplementing with coconut oil in addition to his medical treatment.
Of course safety - of him and of his caregivers - is paramount. If you need a sedative to keep him from hurting himself or others, then you need it. No one wants to drug Dad without need, but sometimes there is indeed a need for it.
You have my compassion. This is not easy. Keep doing your best, and maybe find some respite caregivers or Adult Day Care in your area so you and your mom can have the occasional break to recharge and make sure your own physical, emotional and spiritual needs are being met.