Question

Question #63b75

Answer 1

Technically speaking, "Chrises's" would be the better option.
In my opinion, you should avoid the situation completely by referring to them separately.

Explanation:

I was taught that one should only use s' to show possessive when the noun in question:

1.) Always ends in S
2.) Contains the long E sound twice

For example: the possessive form of the name Demetrius would be Demetrius'.

Following this rule, Chris and Chrises do not meet the requirements for s' due to their lack of long E's

However, many people—including some universities (see https://www.gallaudet.edu/tutorial-and-instructional-programs/english-center/grammar-and-vocabulary/five-ways-to-use-s-at-the-end-of-a-noun-or-verb for their guide)—believe that apostrophes are appropriate after any possessive noun that always ends in S.

Following this rule, Chris and Chrises do meet the requirements for an s'.

In the end, you can use either one, and almost no one will tell you you're wrong. However, you may consider asking your English teacher if he/she has a preference before you put something like this in a report.