“Is it possible for a court to overturn a properly held vote of the people?”
Yes, a court could overturn the vote of the people of Washington State and Maryland to grant same sex marriage rights to gays.
And, if the voters of Vermont elected to force everyone in the state to become a vegetarian and ban the sale and consumption of meat, a court could overturn that decision of the voters.
But there have been dozens of other states to pass same-sex marriage prohibitions and have their decision enter into law. How can what is untouched by judges — supposedly just fine — suddenly be found to be wrong.