What. Things. Did. We. Learn?!

[Trekker4747]

Don't sell Mustache Dad short. When he hugs her we do see him react, he pulls his arms back a bit and has something of a subtle, mustache-y, "WTF?!" look. But at this point he's seen a boy his known his whole life turn into a giant CGI wolf and has already noticed "some" differences in Bella so he's decided "Screw it!" and go along with it.

In fact, I think "screw it and go along with it" was pretty much Billy Burke's entire MO during his tenure in these movies, especially the last two.

[Darth Geek]

So apparently everyone is concerned about Renesme being a half vampire mortal, and NO MENTION of the fact that she will eventually mate with a werewolf and have a baby that is even more of an abomination! Maybe that one will be stop motion animation instead of CGI.

[Trekker4747]

Well, I dunno, Renessme is a hybrid of two different species, therefore she's likely been born sterile.

[Darth Geek]

Well, I dunno, Renessme is a hybrid of two different species, therefore she's likely been born sterile.

The UNDEAD VAMPIRE isn't sterile, why would she be.

[Trekker4747]

The UNDEAD VAMPIRE isn't sterile, why would she be.

I'm about to put more thought into this than Stephanie Meyer did, but roll with me.

We could "argue" the "venom" in vampires basically is a place-holder for all bodily fluids. It "lubricates" their stone bodies so, in  a way, it acts as "blood" carrying the nutrients and such they get from sucking blood from humans (or animals as the "vegetarians" do) to all parts of their bodies, it acts as a literal venom infecting others whom they bite and it acts as, ahem, genetic material.

Vampires we could also liken to being a different "species" -I believe some Twilight "extended universe"/author comments supports this- more than they are the terrors of myth and lore we're all familiar with.  They're closer to being like the mutants in "X-Men" than they are undead demons of death.

Now in real-world genetics when ever you mix two species of the same genus you create a hybrid and most of the time this hybrid is sterile. (This is one of the ways seedless fruits are made.)  So that's the rationale I'm going with, Bella (was) a human and Edward was a vampire. Both the same genus (Homo) but different species (-sapien and -lamia) they can create offspring but that offspring being a hybrid of two different species is going to be born sterile.