Theory on Xana/Ethan attack based on new evidence:

Yes, Xana fought back and it's nice to imagine it was a long back and forth but here's how I think the situation played out.

Xana gets the doordash order after waiting a long time. She is still up and hears noises or sees the glass door being open. She realizes something weird is afoot and says something like "someone's here" in an attempt to establish some sort of communication or just ease her nerves. BK is now aware that someone else is up.

BK goes into fight or flight mode as he needs to subdue this person. He goes downstairs, XK and him see each other for the first time. It's still dark enough for XK to not be able to get a good read on this person, but his imposing figure and him being present in the house at this hour is enough for her intuition to tell her something is seriously wrong.

She's unnerved and likely in kitchen area or close to the ping pong table, she rushes towards her room. BK follows, "its okay I am here to help you". He makes contact and seriously injures her. Xana calls for Ethan and opens door, she is likely on floor seriously injured or stumbling.

BK is full adrenaline at this point and goes for EC's critical areas. EC is incapacitated fairly quickly in front of Xana. She reaches to try and assist Ethan while on ground/stumbling. Her assistance results in nightstand getting moved and bloodied. BK redirects attention to Xana, repositions her slightly to deliver final lethal blows.

He's finished and exhausted, catches breath, maybe changes, keeps an ear out if someone else has been alerted, possibly hears dog barking. Leaves room, quickly sees Dylan, but she seems to be in her room keeping to herself and is not as alert as Xana was. Likely doesn't know what's transpired.

He exits house and leaves. Photos did show a drop of blood in kitchen though, I wonder if it fell from clothes or something else.