Are the ভোকালয়েড related অথবা what?? o_e

Okay so from what I heard... Miku, Len, and Rin are Kaito and Meiko's children.... but there's so many Kaito/Miku pairings and Len/Rin, is that some crazy incest অথবা what?? XD অথবা are they even related??? I'M SO CONFUSED my friend tried to explain it to me and I do not understand XD