In which we return to Questions left Unanswered, or in this case, Unasked;
OR
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.
I just read an old Chinese story about a goblin king who could only be killed by having his hair cut. One of his wives beheaded him with his own hair (ew!). That might explain a lot about Jareth's 'do!