Somebody helped me on the Dutch forum. For everyone seeking the same, i translated the recommendation from there:
-make the subdomains at your webhost
-Install on each subdomain a own version of WP
At this installation you use the same ‘wp-config.php’ (DATABASE etc.) with one important difference: give every subdomain / wp-installation a unique ‘prefix’!
For instance:
default wp-prefix: ‘wp_’
subdomain1: ‘paris_’
subdomain2: ‘amsterdam_’
etc.
now you can give every subdomain a separate theme/lay-out.