My father is 90yrs old, he is dementing but able to take…

My father is 90yrs old, he is dementing but able to take care of himself with family assistance and some agency help. His wife, my stepmother, is in permanent care and her wellbeing is the responsibility of her oldest child. My father gets confused about
some things, which can cause him anxiety and stress, which is harmful to him. My focus is that he should not be put in any situation where this can occur. He is most of the time happy and content with his life. The house is in joint ownership with his wife,
about to be changed to tenancy in common. Not much remains in the house of my stepmoms personal items, her family have come and removed items they consider are hers at their leisure. The problem I wish to ask is , because he is elderly and suffers from some
dementia, I have requested that I be informed when they wish to arrive to do this. This has not happened, it causes my father some distress, as they have also come around when he has been not at home as they have the key which belongs to my stepmom. I have
since had the lock changed at my dads request. My question is, in the circumstances, how much legal right does my father have to request they make a time to do this with him, so that I can be there to prevent them causing him harm. They may not mean to do
this, but in my fathers mind, he feels that his home is being invaded. My requests for understanding and allowances be made for his age have gone unheeded even when I have been very condemning of their disregard.