I feel rather sorry for the over 70's. If they are telling you that life was better for them before mass immigration then that is their truth. To them, life was better when they were surrounded by people with whom they had a lot in common. I think it's extremely disrespectful to dismiss someone's genuine experience because it doesn't fit in with the pervading politically correct rhetoric. This is their truth, your own truth is different, accept it.
I was educated during the 70's in London and there was a low ratio of non-white pupils in our school. If you were to approach those pupils now I am sure they would tell you their life experience has improved since they are no longer the odd ones out (and I was close friends with two of these pupils and so can tell that they very much felt this way). Their truth is very different to my now departed Nan's.
Mind you, I'm not so certain that my Nan was rascist as she seemed to hate everybody equally! Especially the homeless.
I think you are extremely ageist to dismiss a person's "truth" due to their age alone. Old = ignorant? Not on!
Interesting too that no-one has mentioned Citizen Khan when discussing Alf Garnett. Rascism is not a white scourge. The most rascist people I know are my middle-aged Hindu friends who hate Islam and black people with some venom. Do I call them out on it? You bet I do. We agree to disagree and we get on with it, which would be my advice to those "disgusted" by their elderly relative's views.
Incidentally, at the risk of highjacking the thread, I find that the most persecuted groups in today's society seem to be the travelling community (Romany and Irish) and Bi-sexual people, but I see no threads lambasting those who persecute them here. How very odd!