HONG KONG — Over the past three years, Zhou Wanhui, a Hong Kong resident, has visited her parents in China just three times. Though they live only two hours away by train, Covid restrictions made it so difficult to cross the Hong Kong border into mainland China that one of Ms. Zhou’s trips included a three-hour flight to Shanghai and nearly a month of quarantine in two cities.Families like Ms. Zhou’s — kept apart for weddings and funerals, birthdays and graduations — are finally preparing for less arduous reunions.On Sunday, China fully opened its borders for the first time since the coronavirus pandemic began, welcoming visitors without strict quarantine requirements and allowing its citizens to go overseas once agai …
