It is better to think of each post as a separate things.
You would only add data to the apartment post that is specific to that apartment, and this would not include anything about the resident.
The same for the resident, it would only include information specific to that resident and nothing about the appointment.
These would be linked using either a relationship field or a post object field, based on if you want a 1 to 1, many to many, or 1 to many relationship. There is functionality for this in ACF and also some 3rd party plugins, depending on your needs, it is refereed to as a “bidirectional relationship“. This only works in the admin. You cannot create a post of the related type while editing a post (There is a 3rd party plugin that can let you do this https://www.acf-extended.com/features/fields/relationship)
The posts on each side of the relationship are not “aware” of the post on the other end except to this bidirectional field. One post does not know what content the other post has and the data is not automatically shared between the posts.
The above is in the admin only. In the template for each of these post types you would get this field and then use what is returned to get values from the post at the other end of the relationship. Doing this is covered in the relationship field documentation https://www.advancedcustomfields.com/resources/relationship/
