Could he have Parkinson's too?
I'm not a medic and am very wary of careless comments. But... My husband had cognitive difficulties which were getting worse; he then developed twitches in his eyes, and tremors in his legs. In due course, after much testing and exploration, the (wonderful) doctors at the National Hospital for Neurology and Neurosurgery in London diagnosed an atypical form of Dementia with Lewy Body. This is related to Parkinson's but affects a different part of the brain, as I understand it. The cognitive trouble and the tremors have got a good deal worse, as has the lack of facial expression (no hallucinations thank goodness) but Sinemet, recently begun at low dose, has helped quite a lot with the tremors.
Might it be worth asking your local people about the possibility of DLB? I gather it's frequently under-diagnosed. One important reason for obtaining a diagnosis is that with DLB many antipsychotic drugs can be extremely dangerous.
I hope this is useful and not either alarmist or misleading. I wish you good luck.