Thank you Till.
I assigned the IP to all websites. But I still have the weird problem that independently from the entered domain only one (my joomla page) is opened. Except when I use the prefix https:// for my ssl website - Than the website will be opened. Any ideas?
I associated the domains with the IP address of my server in the host file of my windows client (C:\Windows\System32\drivers\etc) to access the websites. I do not think that there is something wrong as it worked fine without SSL.