If a person's name ends in the letter "s", you could still use the apostrophe "s" to indicate ownership. So, if the person's last name is Watkins then add an apostrophe and the letter "s" to show ownership - Watkins's. However, it is also correct to just use just an apostrophe in these instances - Watkins’.
For a plural possessive, you need to make a noun plural and use an apostrophe. For example, for the word girls, add an apostrophe at the end of the word girls = girls'.
For nouns with an irregular plural form like children, add an apostrophe then “s”. So, if you are talking about two women, then you would show possession by simply adding an apostrophe and the letter "s".
