When Finlay sprays the carpet for blood, the whole carpet is blue s where no furniture was meaning it had to be soaked. But the furniture only had small blood splatters, so that clearly couldn't be the case.
At the beginning of the episode, a crew member's reflection is seen while passing by the guest teen
male star.
When given Henry's experience in DNA searches, narrowing down the blood spatter contributions should have been more precise. Had the female been the mother, the male contribution would have 13 chromosomes in common if it was the son. If it was the father, it would have not matched at all, unless the parents were siblings. Had the female been the daughter, the DNA would have shared 13 chromosomes either way, except for the sex chromosome, which she would not have shared with a male sibling.