Here is a learning support on joint possessives‘ cribbed from Paul Brians’ Common Errors in English Usage.
Professor Brians does a nice job of explaining how best to handle this tricky construction and make it sound proper and read the same way. You will not that joint possessive constructions are trickiest with pronouns.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.
