I may try to help you to find more information about your ancestors. At first it is important to find the right location your ancestors had been from: To my knowledge there aren't any "Gruenburg" or "Zelona Gregora", but many "Gruenberg" in Prussia (esp. town "Gruenberg" in Silesia, nowadays "Zielona Gora" in Poland). Also it is important to have more information about the confession of your ancestors.
If you are still looking for further help, please contact me by e-mail.