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.