Okay, I just had the weirdest freaking thought right now and I want you to tell me what you think about it:
What if (because Sora, Riku, Kairi, Terra, Ventus and Aqua are connected) could it possibly be:
Ventus=Sora's father (Explains why Ventus looks like Roxas)
Terra=Riku's father
Aqua=Kairi's mom
?