[Thengise Greenleaf of Mirkwood]

Hmm, I was wondering how it is that Thranduil and Celeborn are related, if they even are? For together they called Mirkwood, Eryn Lasgalen or Wood of the Greenleaf's. Is Thranduil in any way related to Thingol and how was it that he became king of Mirkwood? I was just wondering about those questions and would greatly appreciate it if anyone can help.