the FATHERs are always very closely connected to either the eldest daughter or the youngest daughter.
your respectable mother being either have lost the force from her centripetal pivot making her feel 'alone' which is making her in state of decline of realities around, & thats very understandable,.
like in other thread you shared your father being WORKHOLIC occupied all his life have to make choice preferred time to family over his work.
Now all of you have to devise a schedule to be present around your mom in order to give her quality of life back make her comfortable so she let go of her father'. it will take time, and reconnecting to ALLAH (swt) medication will also help, but the biggest help comes from Almighty & The Family, only.