There is a grammar principle here:
Use each other with two; use one another with three or more.
Remember that, when making a word possessive, everything in front of the apostrophe has to be a word. So when these are made possessive, it has to be each other's and one another's since there isn't a word "each others" or "one anothers."
...John and Joe had each other's phone numbers.
...They all had one another's phone numbers.
Happy punctuating!
Margie