What Causes Loss Of Memory Along With Cognitive Thinking?

yes my fatherinlaw has been told he has about 12 mo. or less by opting out of surgery for a congenital heart problem complicated by blockage in both corrated arteries. he is 90 yrs. old and has tremors memory loss and bouts of cognitive thinking loss for a intelligent person. recently he told my daughter he sees people (a man and a little girl during the day ) and accepts it matter-of-factly which is bizarre for him. He and his wife (are both going down hill rapidly but want to continue at home . we don t know if and when that no longer becomes a choice . but her dads recent hallucinations daily has thrown up a big red flag as he was the most stable of the two.