I find it a little odd that your daughter and son-in-law didn't say hullo. Next time that happens I would say cheerily, "Well, hullo to you too".
As they have a key, if you would prefer them to ring the door-bell before using it, say so. Either make a joke of it, saying you want time to put your teeth in or something like that, or say that it may be silly, but just hearing the door opening made you nervous.
But apart from that, I too have noticed for years that as soon as you reach retirement age a certain number of people do start treating you as if you were incompetent.
I remember remarking to my aunt, an intelligent lady, that I would find it annoying to be spoken to as if I was mentally incompetent for no other reason than that I had reached the age of seventy. She laughed and said she found it very tiring, but there didn't seem to be anything you can do about it.
My father was more forthright, saying, " I may be old, but I'm no daft, ye know." anytime anyone tried patronising him.