I know they've taken him in, for whatever reason. Though I haven't read the novellas admittedly, I really don't think it's practical to say they adopted him, as that would hint toward their relationship with each other. And I know they purposely left their relationship ambiguous and open for interpretation (for whatever reason). So taking him in and caring for him is about all that can be said, since their meaning of "family" together is apparently mostly just a relation of deep friendship.