Not a question, but a correction
This is a great site, which I recommend to my students.
However, on the apostrophe for possessives with nouns, you omitted one rule:
When you have a compound subject, you add 's to only the last subject if the object belongs to all subjects.
Ex.: Mary and Paul's mother. = Mary and Paul have the same mother.
When you have a compound subject with multiple objects that belong to each subject, you must add 's to each subject.
Ex.: Mary's and Paul's mothers. = Mary's mother is not Paul's mother.
That is all. Thank you.
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