The main and key limitation to this ability is that a blood relative must be alive to keep the immortality. An adoptive family member or a relative by marriage would not count, but the family member does not have to be present, merely alive. Another limitation is that the degree of relation cannot be too weak - first cousins would still work, but much beyond that would not. While the relative remains alive, so will Dani, Lee, Addison and Sheridan. They will heal from every injury, wound and illness without even a mark.