In the case of Siamese twins the separation can come much later still. Are there even cases where brain matter is shared and separation is not possible. Lots of complicated scenarios around personal identity and individuality for sure. But are you saying these situations prove Catholics are wrong to hold that life is sacred from conception?
That because individuality may not always be defined at conception, therefore Catholics are wrong that life is sacred from conception. Have I understood the argument correctly? How does it logically follow?