My mother is 90-years-old and independent, my father is 94-years-old and has Alzhiemer's. Can they be in independent living together?

Mom is very independent and cares for Dad each day with help from daughter on regular basis. She is getting too fragile to handle him but we live in separate homes and I feel she is getting very depressed but feels she can do it all. They have small income from working and I know they do have long term insurance. What average cost would it be and can they be together?