views - get teasers of "related nodes" referenced in entity fields on current node
Don't use an Entity Reference relationship for this, but rather, change your Show: to "Fields" and add the referenced entity field. Then you will be able to set the "Formatter" to "Rendered entity", and the "View mode" to "Teaser". 

You may need to add a contextual filter or set this up as an attachment display rather than a block. 

I can post a few screen shots if my answer isn't clear.