I'm seeing a tplink modem self signed certificate, that probably means that you're not forwarding port 443 through to your actual server so it's just your router that's responding.
Regarding ServerName and ServerAlias, you need to include all identifies of your site, so if a single site is known by 3 possible domains names they all need included as either the servername or an alias.
Each site then has it's own *.443 configuration section that says which servernames +aliases it responds to and which certificate file to use.