It was the three major houses: Raith, Malvora, and Skavis. It's implied there are also some minor houses that haven't been named:
As to the number of vamps there:
We then get a number on how many are seated, and that is about a hundred:
There's some ambiguity there. It may have been only a hundred total after all, or there may have been some vamps standing instead of sitting. In any case, most of them were only the "leading members of the three major Houses", which would mean there were a bunch of Whites who weren't in attendance.
I think that maybe you’re looking in the wrong place. I think thank when Thomas initially tells Harry “what he
can’t tell him about”, he describes it as a gathering of a hundred of the most powerful vampires of the White Court. And I’m assuming that would be
politically powerful. So the number of attendees was probably the proverbial tip of the iceberg.
There is an interesting idea lurking around this conversation. If it is the first fatal feeding that turns a white, does the infant who kills his mother during gestation come out a full fledged vampire?
And this is covered to some degree in PG at the Fool Moon Garage.
I suspect that you’re reading it wrong. If a fetus killed it’s mother by feeding, then it wouldn’t be born. I think that what is implied is that the feeding weakens the mother to the point that she doesn’t have the strength to handle the physical stress of childbirth. Making it a 50-50 proposition.
I'm further going to suggest White Court vampire who was pregnant could bolster her own reserves simply by feeding more often to strengthen herself. That seems pretty obvious to me.
I’m pretty sure that Thomas was referring to a 50-50 chance for
mortals—since he was, after all, directly referring to Justine’s situation.
I agree, but if he were, she shouldn't have gotten pregnant.
Exactly. If ya’ll don’t mind, I’m going to suggest a different tack. First I’ll point out that the naagloshii referred to Lara and her sisters as phages attached to a rotting meat sack (iirc). But he/it was speaking to
them. That implies that their consciousness is the phage, and the body just happens to be along for the ride. Thomas referring to it as a “demon” is just a figure of speech, distancing himself from his inherent nature.
More importantly, I’m going to refer to the fact that Thomas states not only that they “took precautions”, but that his kind are “all but infertile”. In essence, a very low sperm count for males. I’m not going to speculate what the actual mechanism is. Nor am I going to question that Thomas and Justine took effective precautions. I'll take that at face value.
Instead, I’m going to go a different direction.
I’ll point out that throughout the series, there have been random events that have happened without explanation. The car that rear ended Harry, and all he concluded was that it was a crime of opportunity. Karrin’s car getting blown up, which he tried to attribute to the various villains of
White Night, but it doesn’t quite fit. And on the flip side, times like when Marcone shows up out of nowhere with a Valkyrie—at the exact moment that Harry is destined to die.
Or, most specifically, when in
Proven Guilty, after Harry has used Little Chicago for the first time to find Molly, Bob discovers that Little Chicago had been “fixed” with so that Harry’s head wouldn’t explode—then it was returned to it’s original state, with the damaged coupling. Implying that someone not only knew about Harry’s lab, about Little Chicago, but had the power, knowledge and access through Harry’s wards to fix (and unfix) it.
So I’m going to suggest here that someone, some outside force, meddled…to make sure that Justine got pregnant.
Not going to speculate as to how or why, positive or negative. But it seems to me that particular leap is a whole lot more likely for Jim’s style than… “Oops. It was an accident”.