A long time waiting for an update so I'm assuming you've abandoned this excellent story for some reason. Too bad really, it has lots of promise.
As a threesome, this story would work, so in the back of your mind, I hope that is what you are/were thinking.
With Hermione and Luna sharing a bed at least some times, I think this would appeal to Harry as a good thing if he decides to keep both girls as girlfriends/lovers/wives.