ok so the vampires are meant to have no blood because they have no heart right. but bella and edward have sex which doesnt make any sense so how can they do it

No No No. Vampires are full of blood, of course. I mean, they live off of it (animal or human). They have hearts, but they've stopped beating. And they have sex because they still have human desires. They're just suppressed by thirst. Meanwhile, if you mean...how is Renesmee produced, the answer is in Breaking Dawn. Every human function is still the same for male vampires, just as humans. Male bodies don't change much..and because Edward was frozen at the age of 17, he had all the right parts to make a baby. Bella was a human..a changing female. Ergo, she had all the "working" parts to produce and carry a baby.

well here is sth that stephanie said abou it.. it's too long to post it so here is the link: link

also you can check it here: link