show fields after adding joins in hook_views_query_alter
If you want view to show your fields, you should not use a hook_views_query_alter. instead you should implement hook_views_data() to describe your audience_node_og_mvh_ti table to view and be able to use its columns as fields when building your views using the UI.

You can however access your view's query results in an hook_views_pre_render() implementations to add your additional field to the output.