What does the end stage of Alzheimer's look like and how long does it usually last?

My Dad is 87. We took his driving priviledges away 2 years ago, then he fell. He was int he hospital and then skilled nursing for 5 1/2 months., Before he fell, he started getting lost in his house. After he came home from skilled nursing, he did not recognize his home or us as his family. He did not know us in the skilled nursing at times either. He has gotten to the point of not knowing my Mom. He gets really irritated at her. She gets very tired. she is 89. When he was in the hospital and skilled nursing, he would get really confused and go bullistic on us and we had to watch him 24/7. We would not allow the nurses to get near him. We would handle and difuse the situations ourselves. There was a family member with him at all time. I am afraid that if we place him into a nursing facility, he would really get confused. My Mom would not leave his side either. My sister lives on the property. Maybe 50 feet from them and is always there when she is needed and then some. I go down on the weekends to help. He is incontinent, he gets feces all over himsel and the toilet. He gets really rude. He would never hurt anyone of us, but he gets really verbal. We do not take his actions personal. He is really weak in his legs. We now use the wheelchair when we go and he has to walk any distance at all.