I have created 5 name servers (NS records) in my domain DNS entry with host names as
ns1.<mydomainname.com>=>NS1.DYNU.COM
ns2.<mydomainname.com>=>NS2.DYNU.COM
ns3.<mydomainname.com>=>NS3.DYNU.COM
ns4.<mydomainname.com>=>NS4.DYNU.COM
ns5.<mydomainname.com>=>NS5.DYNU.COM

But when I use these 5 own name servers for other domains it is not working. please help.

We noticed that you have already set up 5 A records for ns.onesolution-kolkata.com to point to Dynu name server IP addresses. Please change the name servers at your current registrar to the following:

ns1.onesolution-kolkata.com
ns2.onesolution-kolkata.com
ns3.onesolution-kolkata.com
ns4.onesolution-kolkata.com
ns5.onesolution-kolkata.com