XML sitemap Drupal 7 for multi-lingual & multicountry site

Hello all,

We need help because we are are struggling for a while with our multi-lingual and multi country site.
We have 3 domains and each domain has 2 or 3 languages (see below).
The default language is English (common to the 3 domains).
The 2 other (local) languages are not properly indexed into Google.
I am confused with all comments and changes that I read.
I have three questions:

1) Should we create specific sitemaps by languages?
2) Which module(s) and patch(es) would you install for this?
3) How to make a language more important for a specific country?

Thanks community !!

www.abcompany.be/fr
www.abcompany.be/nl (more important language)
www.abcompany.be/en

www.abcompany.fr/fr (more important language)
www.abcompany.fr/en

www.abcompany.nl/nl (more important language)
www.abcompany.nl/en