Teach me how to customize some php code Wordpress + ACF user relationship field

Basically I need to allow an array of multiple users IDs to be validated with the current logged user. If you see line 119, I am using acf user relationship field, and then in line 120 the id with the user needs to match the current ID for a logger in user. 1. The code works only if I select one user at the time, but I need to select more than one user, so the code needs to be modified to verify different users. 2. Lines 203, 204 I need to customize this message : one for a not logged user and another one for a logged user without the permission to view the page. ---- Open to other options like : - Content restriction by role (I find this will be easy than selecting multiple users per page)