I think having them already be witches might be jumping ahead a bit too far.  Perhaps the opening post could include a small "excerpt" from the funeral, but starting afterward would be fine by me.  I know in James' case it's going to be enough of a hurdle just being forced into close contact with family again after living the past years as something of a hermit--hell, his brothers probably haven't even<em>seen</em>him in years.  I'm not saying we drag on introductions, but some time to acclimate would probably be necessary before dropping the whole "You're a witch!" bomb on them.