The rule is that “each” will always be followed by a singular. “John and Mary promised to love each other forever. They agreed to take care of each other’s wellbeing above all else.” The apostrophe is used to indicate possession, and it comes before the s, not after it. If we don’t prefix “other” with “each”, we can use it in the plural form.

The correct spelling is each other’s, not each others. The apostrophe and “s” help show possession by indicating that something belongs to both parties involved.

The answer depends on whether “others” refers to the singular or plural possessive. If you are using each other (singular), then it is “each other’s.” If you are using the plural, then the apostrophe goes after the “s.”

If you remember that everything in front of the apostrophe has to be a word, you know that it cannot be each others' because there is no such word as each others.