Be The First!

I've read Swordspoint once, a million years ago, but this is the first I've heard of Tremontaine. So I'm sorry, but I can't really give you an educated answer here. Ultimately I'll leave it up to your judgment. That said, the rules about franchises is that if the parts are separate enough to basically be different series, then it's fine. But not if they're closely connected, with the same characters and continuing plot. I'm taking it you were planning on writing about the new characters you mentioned...? If so, I think it's fine!