Does Zhuhai, Guangdong have an Airport ? Are there flights to and from ZH to Beihai, Guangxi ?

Yes, there is a Sanzao Airport in the city. But there is no direct flight between the two cities. If you wanna travel by air, I suggest you take a plane to Nanning first. At Nanning Langdong Bus Station, you can take a bus to reach Beihai in about 2.5-3h. For the back journey, you can use the say way.