I like this! It has a lot of potential for really great character, and I already feel charmed by the world. It's not an epic quest, but it feels meaningful somehow. If I were you, I would try to get your players emotionally invested in helping out Sophietta, and maybe making her grandaughter a character that your players have opportunities to interact with. I wonder if you could rewrite it with Hasartain as the BBEG? Or maybe that's a bit cliched. The idea doesn't make much sense with the way you've written it now, you'd basically have to have him and Sophietta separated by some circumstances...Maybe she asks the party to take her grandaughter on a quest or two? Could you write some sort of conclusion based on that?
There's certainly value is having Sophietta's granddaughter join the party. It could be a very epic way of introducing a new player character. You'd have to be careful so that the Red Set wouldn't be too powerful or too weak. I'd be cautious about giving the party an escort quest. They can be difficult as the main focus switches away from the player characters.