SSL is a IP based protocol, so when you use https, then the only ssl based website will get opned that is defoned on that IP. The domain name does not matter here.
If you use http, then apache should show the website based on the Domain name. You should ensure that all domains point to that IP in dns and that they have a a record for the domain and a a or cname record for the www subdomain and that auto subdomain www is enabled in the website in all sites.
The behaviour that I described here is the normal behaviour of apache when you use ssl, for that reason you use normally a dedicated IP address for the SSL website which is not used by any other site.