Techsky, you will need to create the nameserver entries pointing to your VPS IP, while only one VPS you should have 2 IPS as many registrars will not accept them on the same IP for two names. It does NOT add redundancy to have them on two IPs being that it is one VPS, but it does get past the "you are using the same IP for two nameservers" errors that some Registrar will throw at you
After you add childnameservers you need to wait until they are working, then setup the sites as you would, in cpanel that means going to WHM and making a cpanel account and adding the domains it should serve them up as you expect.
Sorry but I work with cpanel VERY little maybe someone else can step in and assist there, as for pinging, yes you should be able to ping ns1.yourdnsserver.com as created at DirectI. It may take up to 72hours.