Stop! Grammar time.
If you watch The Bachelor (which I most definitely do not), you probably hear the following phrase ad nauseam during the “confessional” videos: “Topher and I’s relationship is really special. I think he may be the one.” Then the next girl comes in and says literally the exact same thing.
When you catch yourself saying something similar, don’t beat yourself up. It seems like the natural thing to say — in the "Bachelor" example, Topher and “I” share a relationship. In order to make Topher possessive (which he totally is, by the way), you would add ‘s: “Topher’s.” Pretty easy.
Now, to make “I” possessive, you actually get rid of it altogether and replace it with “my.” “My” is the possessive form of “I.” So, to correctly speak or write this sentence, you would say “Topher’s and my relationship is really special.” I know that sounds awkward, but it’s correct. If you want to avoid this awkward linguistic limbo, you can simply say “Our relationship is really special.”
When you are referring to two or more other people who share the same thing, you only need to add ‘s to the last person listed. So, if you’re a contestant on "The Bachelor" and you are referring to another girl’s relationship with our boy Topher, you would write/say: “Topher and Krystyn’s relationship makes me totally want to hurl. Please pass the champagne.” Even though that’s a terrible way to spell Kristen, it’s a grammatically correct sentence.
In the case of multiple owners who have separate ownership, you add ‘s to each name. Krystyn and Ashlee each have a different relationship with Topher, so if you were griping about their relationships, you’d say something like: “Krystyn’s and Ashlee’s relationships with Topher make me totally want to eat my feelings. Please pass the ice cream.”
This grammar terminology of compound ownership is called compound, or joint, possession. And, while joint possession is still illegal in most states, good grammar is always welcome.