While not much is known about the relationship between Castaspella and her brother Micah, it can be assumed that she cared for him deeply, for when he is brought up in conversation she becomes saddened by his memory.
Additionally, In episode 7 In the Shadows of Mystacor, she mentions that she and Micah trained together.
She is shown to be a very overzealous aunt, a woman who wants nothing more than to be appreciated by the family her brother left behind. It was mentioned that she knits sweaters for her niece, and socks for Bow, something that the former doesn't seem to enjoy, though she'd never say it to her face. Additionally, she expresses concern about how Glimmer had very few friends in the past, saying that she even dared to believe that Bow was made up before Glimmer finally brought him by. She adores spending time with Glimmer and her friends and elects to show them around Mysticor again just to spend more time with her little niece.
Her relationship with Angella is very vague. She briefly mentions during the tour she gave Glimmer and her friends that Angella refuses to write back to her, despite all the letters she's sent to her over the years. But other than that, besides being her niece's mother and her late brother's wife, their relationship remains a mystery.