From Ashleigh Banfield's program, info she says came from "a couple of sources familiar with the investigation" on "the order" in which the four of them were killed (also the "manner" but it is very graphic as she warns).
So: unnamed sources = take it with a grain of salt, or if you don't care for AB's show, as mods have reiterated, please just "roll and scroll".
Paraphrasing, AB's sources say:
Kaylee and Maddie were killed first in Maddie's bedroom on the 3rd floor.
Ethan was killed next in the area of Xana's bedroom door on the 2nd floor.
Xana was killed last in her bedroom and she had wounds that indicate she fought the attacker extensively.
Sources: Idaho victim Xana Kernodle was killed last and fought back | Banfield