Schroeder Family IN Germany

Hi
I am looking for my great-great-great-great grandfather's family who are in Germany. From my findings he was a solider from Germany during World War 1 which was send here in Samoa an Island in the South Pacific, my papa didnt return back to Germany after the War but he married to a Samoan lady and have six children and two of his children went back to Germany to look for his family those two children are: Anna and Heinrich ever since they left the island they didnt return back nor we hear any word from them.

I hope you or anyone can help me