Many people use “I’s” when they have two subjects and they want to use a possessive form. “My …. and I’s….” is grammatically incorrect in English and should be ”My …. and my…”
My wife and I’s car is a Toyota.
My wife’s and my car is a Toyota.
My brother and I’s cat is called Jessy.
My brother’s and my cat is called Jessy.
This construction “My … and I” is common in English and for that reason, it is very tempting to add an “s” after “I” because that is often what you do to make something possessive.
It is much easier to use the possessive pronoun “our” in most examples although it may not explicitly state who “we” are.
What is I’s supposed to mean?
“I’s” is supposed to be the possessive pronoun of “I” but the correct possessive pronoun is “my”
If you mix nouns(my wife) and pronouns(I) in English then you need to give each subject its own possessive form.
When can you use I’s?
“I’s” is incorrect. The correct possessive pronoun of the subject “I” is “my”.
You may often hear native speakers say “My sister and I’s car” and it may even sound right to you because “My sister and I go to school” is correct and very common in English.
If you wish to make “My sister and I” into a possessive statement that together you own something, then you need to say “My sister’s and my….”
I’s or my? Which is correct?
“My” is correct as it is the possessive pronoun of the first person singular.
Another grammatical mistake is the idea that “I’s” is the contraction of “I is’ which is of course incorrect as the correct conjugation is “I am”.