Maybe moving our dad from one nursing home to a better one. this means hed be leaving his sister. theyre both early dementia and dad has aphasia also. he says he wouldnt mind leaving her but could this change be bad to his type of brain/emotions ?

If you can find a better chronic care facility, go for it. Your Dad may get lonely, but the new staff will likely assist his adjustment. If he becomes depressed, appropriate meds can be initiated. Why not also transfer his sister? Encourage your Dad to have speech therapy and engage with other residents. Also, exercise daily, preferably with others in facility. Have neurologist involved.