How to define another teaser for the second theme?
Problem solves by the following: 


Created DS template for default teaser in 2nd theme: ds-2col--node-article-teaser.tpl.php
Place into it code to define my new node_teaser_mobile to show:  

print render(node_view($node, $view_mode = 'node_teaser_mobile', $langcode = NULL));