Who was in the Hale fire?
Using clues in the show, can we figure out, once and for all, which of Derek's family members died in the fire?
Before we find out the who, we need to know how many.
While researching the fire in season 1 episode 5, Stiles looks through a report listing 8 people found dead.
However, in season 1 episode 4, Derek says that 11 people were caught in the fire.
11 minus 8 means there is a discrepancy of 3 people. BUT notice he said 11 people were IN the fire, not that 11 people DIED in the fire. That means that only 8 BODIES were found. Fortunately, the 3 bodies unaccounted for are pretty easy to explain.
The first would be Peter, who survived the fire.
The second would be Cora, who Derek had always assumed was in the fire but had actually been out of the house when it happened.
And the third person, you might be surprised to learn, would be Talia, as Derek says in season 3 (episodes 15 and 22) that "her claws were all that was left of her". Meaning her body wouldn't be there to be in the police report.
So that leaves the remaining 8 caught in the fire to figure out. Here's what we know:
According to Chris, there were human children in the fire. Children, not child. This means at least 2 of the 8 members were human children.
Next, in Peter's flashback, we see three people (maybe four) trapped in the basement, attempting to get out through the bars. We see one adult man alongside a male and female (unclear whether they are adults or kids). There also looks to be the arm of a much younger child peeking out from under the male with the red shirt.
From here, although we probably can't get a definite answer, we can for sure narrow it down some more.
If any of the children are Derek's cousins, we can infer at least one aunt (who may or may not be Peter's wife). There could also be another aunt+uncle pair.
Derek at one point says there were "normal people" (i.e. human) in the fire. This might suggest a human adult, since Derek easily could have just said children to emphasize the point of the atrocity.
Since Talia was already Alpha before the fire, this would suggest one or both of Derek's maternal grandparents weren't alive to be in the fire. One at least had to pass on the Alpha spark, and the passing of both due to old age is possible.
So, now, here's what we're left with:
1. Human child #1-either Derek's cousin or brother/sister (probably younger, considering there isn't much room for an older sibling to still be called a child as Derek was 16). Depending on who the other adults are, if this is a cousin, they could've been Peter's child or this could indicate that another uncle/aunt of Derek's were there.
2. Human child #2-another cousin or another of Derek's siblings, could be Peter's child, or could point to another uncle/aunt of Derek's
3. Man #1-could be Derek's father, could be another uncle, maybe an older cousin or Derek's older brother
4. Human child #3/werewolf child #1-Derek's younger sibling or cousin, possibly Peter's child or could point to another aunt/uncle
5. Possible Aunt #1-could be either human or werewolf, could be married to Peter or not
6. Possible Uncle that could be married to Aunt if she isn't Peter's wife
7. & 8. Either another aunt+uncle pair or could be Derek's paternal grandparents.
My personal head cannon would probably be:
1. Derek's human cousin-daughter of human aunt
2. Derek's human cousin-younger son of werewolf aunt
4. Derek's werewolf cousin-older son of werewolf aunt
5. Derek's human aunt-his father's sister
6. Derek's human uncle-married to his father's sister
7. Derek's other human uncle-his father's brother
8. Derek's werewolf aunt-married his father's brother
Edit: I didn't notice I wrote Peter's child when I meant Peter 😅
