Alright I know some people have questions about my story and in this chapter I am going to answer them. First of all the reason Nightmare Moon's soul wasn't taken was because she was a part of Luna and she was on the moon for a thousand years therefore its Luna's soul that must be claimed. As for why now its because since she was right there it would save him the trouble of having to go to her while she is in the castle.
And I'll also try to add more spacing so it will make it easier to read. I hope I answered all your questions.