Here is how to show posts, that have at least one common parent with the current post.

Let's say we have two CPTs: Events and Producer,

and they are Related -

Producer is parent CPT, Events is child CPT, Many to Many Relation

There is a Relation meta key - we will need that.

On the Single Template of Events, place a Listing Grid, which shows Events.

In it, set two Posts Query items:

- Meta Query

   Relation meta key IN %related_parents_from|producer%

- Posts & Author Parameters

   Exclude posts by IDs - %current_id%

Then, this Listing Grid will show only Events, that have at least one common Producer with the current Event:

(all Events are shown for the reference)

Hope that helps!