In which we return to Questions left Unanswered, or in this case, Unasked;
In which something else must be explained.
I rather believe the magical community holds less significance with the messy organics of relations, given that in almost any given system, half of them are shape-shifters, mpreg, or otherwise unusual conceptions. Certainly, some of them are... more carnally inclined than others (*coughJadisandDarkness*), but this, at least, should help explain how and why various members of the magical community refer to each other as "aunt", "cousin", and so forth.
One can hope.
Jareth belongs to Henson, Lucas, and Bowie.