I'm sorry that you've suffered memory loss.

I think what's more important is the positive impact you have, just by being there on those special occasions. Many old people don't get that, and they get almost "abandoned" in old age/facility care. It's the little things that count.

I don't think you'll have to "say" anything per say at the funeral, and if anything, you can make reference to how you've visited them on these occasions.