Hi Joris,

well it seems a quite weird and complex configuration so i'm quite lost advicing you about how you can manage all these kind of languages, website domains, menus and related sitemaps.

By the way what you can try to do based on my ideas is the following:

1. Use datasets to restrict menus to each domain. For example create 3 datasets:
- Dataset 1 for menu 1
- Dataset 2 for menu 2
- Dataset 3 for menu 3

2. Combine languages with datasets for sitemap links, so for example:
-trikke.nl will have the sitemap link as: http://trikke.nl/index.php?option=com_jmap&format=xml&dataset=1&lang=nl
-hpv.trikke.nl will have the sitemap link as: http://hpv.trikke.nl/index.php?option=com_jmap&format=xml&dataset=2&lang=nl
-skki.trikke.nl will have the sitemap link as: http://skki.trikke.nl/index.php?option=com_jmap&format=xml&dataset=3&lang=nl

and so on with other languages:
-trikke.pl will have the sitemap link as: http://trikke.pl/index.php?option=com_jmap&format=xml&dataset=1&lang=pl
...etc...

Take care that in the JSitemap control panel you have to get the multilanguage dropdown, if not change the setting 'Sitemap multilanguage dropdown' to 'Show always dropdown'.
I hope you have a standard and correct Falang installation with all languages installed in Joomla. Other than this i can't see solutions to manage all this scenario.

Best regards

John