Apparently it's nowhere near as bad as is made out.
There is a lot of resentment on Joan's part, but whenever Joan is in Paris, or Olivia is in LA, they are known to visit each other.
Yes, by all accounts, that is right.
I read Joan Fontain's autobiography 'No Red Of Roses' a while back and their feud was very much more in the minds of the publicity departments than in reality prior to their Mother dying in 1975.
Sure they do not like each other. This got worse when their Mother died and Joan was only informed after the funeral had taken place. She was out of the country and Olivia informed her via telegram - by the time she got it the funeral was over. Joan never forgave her sister. They also argued over their mother's treatment (she was v elderly and suffering from cancer) They could not see eye-to-eye on anything at all.
As you said Joan does (or did) visit her sister in Paris when she was there. As does Olivia when she is in California.