Family Members (1998 series)
- Ethel Hallow: Mildred Hubble's acid-tongued rival, who always scores straight As in all her subjects, but is also mean-spirited and vindictive, and forever plotting to get Mildred and her friends into trouble, even if it is at the expense of the entire Academy being humiliated as well. Despite her being something of a "teacher's pet" as she knows when to turn on the charm, Miss Cackle and Miss Hardbroom are not truly fooled, and both have no qualms about punishing her whenever she crosses the line. It is also possible that part of her behaviour was due to the stress of having to live up to high family standards - Hallow family portraits adorn the walls of the Great Hall of the Academy, and when asked why she choose to attend Weirdsister College, Ethel simply responded with "I'm a Hallow". As a teenage student at the college, her nasty attitude appeared to have toned down, and though she and Mildred never became intimate friends, she still helped Mildred to save the college - and, by extension, the entire world from a potential apocalypse.
- Sybil Hallow: Ethel's younger sister, who once revealed during a temper tantrum that she was forced to attend Cackle's Academy due to family expectations, which is similar to how Ethel was pressured. Sybil started off at the Academy as a gullible girl who believed her older sister's lies about Mildred, but she gradually learned the truth about Mildred's kind-hearted and heroic nature, and found the strength and confidence to stand on her own as a talented young witch who excelled in music.
- Mona Hallow: The youngest of the three Hallow sisters, Mona is the best friend of Henrietta Hubble and Crescentmoon Winterchild, and an intelligent and friendly girl who enjoyed science.
Family Members (2017 series)
- Esmerelda Hallow: The oldest of the Hallow sisters, Esmerelda is two years above Ethel at the Academy, as well as the head of her year. Despite her student status, she had already established herself to be an adept witch - she set the record for the Academy's entrance exam, scoring 100% for her written paper and 98% for the practical. Despite these accomplishments, Esmerelda is humble and kind-hearted, and always tries to look out for her younger sisters and guide them in the right path. However, it is only Sybil who is receptive towards her advice, for Ethel is bitterly jealous of her due to her being their mother's official favourite, and it is only during times of great crisis (such as Agatha's successfully taking over the Academy) did Ethel reveal how much she truly loved her older sister.
- Mrs. Ursula Hallow: The mother of the Hallow sisters, as well as a former member of the Magic Council. Mrs. Hallow was shown to be an extremely biased and callous parent who played favourites with her daughters - in Maud's Big Mistake, she used a projection spell to attend Ethel's parents' evening appointments as she could not be bothered to come, but she planned to come in person for Esmerelda's prize-giving (which took place the following week). In A New Dawn, it was revealed that Mrs. Hallow had faked signatures on a petition to get Miss Cackle dismissed from her position, for she wanted revenge against the Headmistress for Esmerelda's loss of magic, and when Ethel demanded to know if she cared about her (Ethel's) education, she retorted with "I have a non-magical daughter at home. Do you think I have time to think about anything else?", which demonstrated how little she cared for her younger daughters. Upon the public exposure of this scheme, the Great Wizard revoked Mrs. Hallow's position on the Council, though Miss Cackle pleaded with him to be lenient with her for her daughters' sake. Mrs. Hallow was said to be overjoyed when Esmerelda regained her magical powers, but her relationship with Ethel remained severely strained.
- Beryl Hallow: The grandmother of the Hallow sisters, whom Mildred met when she went back in time (The Mists of Time). She attended the Academy at the same time as the Cackle twins and Mona Spellbody.
- Gertrude Hallow is an ancestor of Ethel's who was Cackle's first head girl.
Family Members (1998 and 2017 series)
- Mr. Hallow: The Chairman of School Governors of Cackle's Academy, as well as the father of the Hallow sisters. In the 1998 series, he is highly skilled with computers and continually tries to get the school to modernise and use technology, which often led to disputes between him and Miss Hardbroom, who believed the school should keep to its medieval-like traditions and surroundings. In the 2017 series, he first appeared in person in Hollow Wood, and was sent by Mrs. Hallow to fetch Esmerelda from the Academy. It was also stated in this series that he has magical powers, and can pilot a broomstick like a true wizard.
In First Prize for the Worst Witch, it was revealed that every Hallow who attended the Academy in the previous two centuries had been Head Girl; there had been thirty-five Hallow Head Girls over the centuries.
Hallow family portraits adorned the walls of the Great Hall of the Academy, including Ethel's grandaunt (mentioned in Art Wars), and subsequently there was unacknowledged yet definite pressure on the likes of Ethel and Sybil to follow in their ancestresses' footsteps and do well. Though this is not the sole reason, it is still highly likely to be one of the major factors for Ethel's singling out Mildred for bullying - a subconscious way of venting her stress from the pressure of always having to be at the top where grades were concerned.
In the 2017 series, during All Hallow's Eve, Ethel met her ancestresses when they came to life from her Family Tree. Apparently, Mrs. Hallow once told her daughters a real story about how a Hallow witch saved her coven by reigniting the coven's Founding Stone, but Ethel had always dismissed it as a mere fairy tale. Nevertheless, she went along with Mildred, Maud, and Enid in search of answers from her Hallow ancestresses, only to end up being increasingly dismayed by the revelations of what kind of witches the Hallows truly were - cheaters who delighted in cursing their neighbours' goats, or transforming other coven members into toads when they outgrew their boots, etc. Ultimately, it was revealed that the Hallow ancestress who supposedly reignited the Stone was not the one who did it, but she just took credit for it! It was actually Mirabelle Hubble, Mildred's ancestress, who reignited the Stone.
- In the Telemovie, Ethel was mentioned to have older sisters and a three-year-old brother - Miss Hardbroom commented that Ethel was “obviously going to be top in everything, just like her sisters”. In the 2017 TV series, Ethel has an older sister named Esmerelda.