If you `ping`, your recursive resolve (like Google DNS, or your ISP DNS servers) will do the recursive lookup for you.
WHOIS data are irrelavant to resolving the host IP address. The SOA will be used to find the primary name server (for an AXFR lookup perhaps), but generally, each NS entry will work in a round-robin fashion and SOA isn't queried.
Most resolves just ignore duplicate records, but I imagine some resolvers may change the "odds" to likely pick the duplicated NS entry.
Finally, most authorative resolvers do not want to spend resources on ANY queries and almost always don't return all records, or like you saw, do not de-duplicate answers.
> Do you know why the name servers are part of the WHOIS data?
The NS returned from the registrar's WHOIS server reflects the registrar's view; the NS returned from the TLD nameservers reflects the registry's view; the NS returned from the zone's authoritative nameservers reflects the registrant's view. These should typically be the same, but can differ.
> why is the name server present in SOA record too?
The NS in the SOA record is used for RFC2136 dynamic updates and RFC1996 zone replication.
If you're trying to debug why a website's setup isn't working, the first step is to see if what the registry thinks the nameservers should be matches what the nameservers in DNS actually are. These can fall out of sync if e.g. the registry's connection to its DNS provider is experiencing issues. This does actually happen from time to time.
WHOIS data are irrelavant to resolving the host IP address. The SOA will be used to find the primary name server (for an AXFR lookup perhaps), but generally, each NS entry will work in a round-robin fashion and SOA isn't queried.
Most resolves just ignore duplicate records, but I imagine some resolvers may change the "odds" to likely pick the duplicated NS entry.
Finally, most authorative resolvers do not want to spend resources on ANY queries and almost always don't return all records, or like you saw, do not de-duplicate answers.