I got this vibe from your description:
[name_f][/name_f][name_f][/name_f]
[name_f][/name_f][name_f][/name_f] In modern day, they’re knows as the “Grim-sisters” and how ironic it is that their last name is dark/mysterious, with all three girls being known for liking horror movies, Halloween, etc.
[name_f][/name_f][name_f]Mallory[/name_f] [name_f]Beatrix[/name_f] Grimstone “M.B.” or “Mal”
[name_f][/name_f][name_f]Heloise[/name_f] [name_f]Carmilla[/name_f] Grimstone “Helly” or “Lou”
[name_f][/name_f][name_f]Cressida[/name_f] [name_f]Alice[/name_f] Grimstone “Cece” or “Sid”