Update!!
I've just got it working.
If I include all Yoast wp_option table keys at wpml-config.xml file it starts working, by being included at polylang strings theme's group.
wordpress-seo strings group has the same keys like it had before which brings a duplication.
This confirms that those keys included at wordpress-seo group never get to action, but they do if in the theme.
However, the strings from the other plugin that don't want to work are also assigned to the theme group.