"Gjúki (also Gebicca, Gifica, Gibica, Gebicar, Gibicho or Gippich) was the King of the Burgundians in the late 4th century until his death in or around 407. He was the father of Gundomar I, Giselher and Gunther."
"The precise relationship with the four named individuals is unknown." 
This is where we run into the border between historical records and the Norse Sagas. There, in the Sagas, relationships are given for the names in question, however, how accurate they are is another question.
↑ Wikipedia contributors, "Gjúki," Wikipedia, The Free Encyclopedia,  (accessed March 21, 2016).