“Individuals'” is the correct plural possessive form of “individual.” You should take the plural form (individuals) and add an apostrophe to the end of it. This shows that more than one “individual” owns an object. “Individual’s” is the singular possessive form.

The word individual’s is the singular possessive of individual. E.g., “Each individual’s bag must be checked before boarding.” In addition, individuals’ is the plural possessive form. E.g., “The individuals’ demands were excessive.” Also, individuals is the standard plural form of individual.