They have similar fruits but not the same.
Boa Marigold has the Hebi Hebi no Mi, Model: King Cobra.
Boa Sandersonia has the Hebi Hebi no Mi, Model: Anaconda.
A majority of the Zoan Devil Fruits also come in different "models" that result in variations of the animal. For example, the Inu Inu (Dog) Fruit has Jackal, Dachshund, and Wolf models, the Ushi Ushi ...
In addition to the other answers, the healing ability of Ivankov's Horm-Horm fruit shortens the recipients life by a certain amount depending on the severity of the injuries. Luffy traded 10 years of his life to recover from being poisoned by Magellan in Impel down.