Mary created a trust that holds the deed to the house. We are all listed as beneficiaries:
Miss Justine Frankenstein
Miss Catherine Moreau
Miss Beatrice Rappaccini
Miss Mary Jekyll
Miss Diana Hyde
Mrs. Arthur Meyrinck (née Helen Raymond)
But it is her house, really. Her father left it to her, along with a moderate fortune. She is the only one of us who has inherited any money. Science does not pay well; mad science pays even worse.