Well. Here is an example. Let’s say I have a server running cPanel and have my old name servers that points to my server. And my users can manage their DNS records from my interface, because name servers points to my server. But if I will make my “vanity nameservers” which points to DO ip’s, how users will be able to manage their DNS records

through my interface? Because name servers will now points to your servers. Please explain in more detail for “vanity nameservers” what I need to configure my server (cPanel) to enable users to manage their DNS records through my interface?

In that case, your users won’t be able to manage their DNS records themselves. Unless you build a cPanel plugin/extension that uses the API to update the records on DigitalOcean, you will need to update the domains yourself.

If you want to use cPanel for managing DNS records (which is preferable in this case), you can set up Branded Nameservers. Keep in mind that running only one DNS server isn’t enough, you must have at least two different DNS servers, so you might want to consider setting up a cPanel DNS Slave.