A very creative story.  I'll be interested to see how you continue it.

I find the possibilities here to be fascinating. Speculating is so much fun before JKR gives us canon information to go on! I also figure that Eileen Prince has to have some familial connections to predominant names in Potterverse.

I take it their last name and which sister is older is unimportant?

So, Harold and Salina take their one son, James, and adopt the last name of Potter, leaving Demi still as Mrs. Prince. Do the two 'families' still all live together? And what becomes of Thomas? Is he just taken out to the woods and left? Set adrift on a river in a cradle of reeds? Given up for adoption to become an unwanted child that becomes a Dark Lord??? Spit it out girl! Is Demi supposed to kill her own second son so the firstborn can inherit? What about Harold [Prince] Potter's son J2... does he get zip, zilch, zero as far as inheritance? After all, he is a third son. How can Harold just abandon Demi, James1 and Thomas?

Why does Harold make so much of Demi for nearly a full year, ignoring Salina, and then suddenly decide that Salina is to be favored? I don't like this Harold.

very interesting beginning. I wondering what's going on and who thomas turns out to be!

I'm having a dense day so I had to read it twice to catch everythign. It's interesting. Oddly enough, I just finished reading "A Handmaid's Tale" by Margret Atwood.