Hmmm... there's certainly a number of things that I like here in this story.
First, I throughly approve of all of your choices of hot women. Good ones all.
Second, I'm thrilled to see another story following this challenge.
Third, you've applied an excellent hook.
On the other hand, there's a number of things I quite dislike here too.
First off, while I whole heartedly agree "Harry" is a ridiculous for a person, that's what Harry Potter's actual birth name is as far as anything we've ever been told goes. Changing the main character's name for any reason other then stealth or amnesia is pretty much a no-no. If they're hiding out because they're immortal or on the run it's one thing. If they can't remember their name it's another. Changing it to something else, unless you introduce a fundamental magical reason that every magical person has to have some kind of fancy name, just looks like you want to make it something "cool" or that you want to distance that character from their canon personality because you won't actually be writing about that person, you're just borrowing traits from them to slip in yet another barely hidden OC.
Second, from all of what I know from DC lore, Supergirl and Powergirl are actually on really poor terms at best. Powergirl pretty much hates being compared to Supergirl in most any way. I've also seen Wonder Woman and Powergirl frequently shown as being at odds as well. Thus Karen saying she's "Basically Supergirl from another universe"...? Yeah, no.
Third, considering you seem to be making little if any distinction between Kara and Karen it makes it seem like you just couldn't pick. Unless there's a story based reason for it, I'd ditch the whole "Peverell" angle and just go with Black and Potter (which as Sirius is still alive doesn't actually work out very well) and only use two of the girls. Karen and Kara being married to the same guy could be used for some incredibly deep and insightful character development after all, and the whole Diana + any man + any third partner at all looks like it would = a really good story.
...unless this story's all about the smut. In which case my primary complaint about this is that you're taking too damn long to get there and this story sucks. Based off of your rating and your writing I think it's a safe assumption to say that your intent lies elsewhere at least for now so your story isn't outright bad, but it is shoddy and can and ought to be a lot better. This chapter doesn't read like it was written by a bad author of any sort, just a lazy one. So do better, because you're more then capable of it.