Another plotline might involve the Potter twins uncovering some long - hidden secrets about Snape's past. They could discover things that make them see him in a whole new light, and this new understanding could change their relationship and the course of events at Hogwarts. For example, they might find out about his unrequited love for their mother in a different context.
A possible plotline could be the Potter twins getting into trouble and Snape being the one to save them, not out of any love for them at first, but because of his sense of duty. As he spends more time with them during this process, he gradually develops a more paternal or protective feeling towards them, which is quite a contrast to his usual cold exterior.
One interesting plotline could be Snape taking on a mentoring role for the Potter twins in a more in - depth way than in the original series. Maybe he teaches them some advanced potions techniques or helps them understand the darker aspects of magic that others might shy away from.