So this is how the damn apostrophe is used for plural possession. It would be nice if spell checkers stopped highlighting this as an error.
Use the apostrophe to show possession. Place the apostrophe before the s to show singular possession.
one boy's hat
Ms. Chang's house
NOTE: Although names ending in s or an s sound are not required to have the second s added in possessive form, it is preferred.
Mr. Jones's golf clubs
To show plural possession, make the noun plural first. Then immediately use the apostrophe.
two actresses' hats
two children's hats
the Changs' house
Read all 13(!!!) rules [here]