You need to install two SSL certificates. One per domain. So you need dns zone for both.
Ask for assistance of your provider, if you don't know how to manage DNS zones for your server. You need to configure bind for multiple domains on your server before, than you can use same IP and DNS zone details for both domains. If you need to do it by yourself, then you will find several tutorials on this by searching via google specific to your OS in use (debian, ubuntu, etc.) Use the keywords dns zone multiple domains