There is a charming description of the Yussupov family in exile in Paris in Princess Tatiana Metternich's book "A Purgatory of Fools"
Princess Tatiana was a Russian aristocrat whose family fled the revolution when she was small. After wandering a bit, she ended up in Nazi Germany, was close to the Resistance and married Prince Paul Metternich. She and her husband seemed to know a good portion of the middle european aristocracy and there are interesting pictures and comments (she tends to be kind, but, I believe, perceptive) about them and some royals, including the Russian imperial family.
Her description of the Yussupovs pictures them while they still lived lavishly although she makes it clear that harder times were on the way because of the Prince's spending and generosity. She admired Princess Zinaida greatly for the qualities which have been discussed.
Princess Metternich's book is fascinating and gives a absorbing picture of a group of aristocrats in Germany before and just after the defeat of Hitler. The Metternichs had to flee the communists--the second time for Tatiana--but fortunately they had a valuable estate in the West.
Tom