CP: Title from relation?
relation_interview_persons is not an array of elements but an object of type ElementQuery. In order to get the results you need to call one().

Keep in mind chances are high there is no related element if that's the case your code will throw an exception.

{% set person = object.relation_interview_persons.one() %} {{ person? person.firstname : ''}}


If date is not a field of type text but a Date field that will throw an exception as well since it's an object and no string