Skin on older people is very dry and can be easily irritated. Dial is very strong and perfumed, so it is very drying and can be very irritating to the
skin. Also, I know that Ivory is supposed to be "pure" and not perfumed, but it is a very harsh soap. It will also really dry out the skin.
I recommend baby wash. I know that it sounds strange, but it cleanses and it is very gentle. It will not dry out the skin, so it reduces irritation. Since I have very sensitive skin, I use it myself, and I can tell you it really works!
If you absolutely must use a bar soap, then try Dove. It is the most gentle bar soap that you can get.