From the moment of divergence they begin to have unique experiences that make their self a different person than the others. 10 selfs. Each with their own end and none of which will be a shared experience meaning they are not the same self anymore.

Identical twins start out as one egg with a shared experience. After separating they become two selfs each unique. Identical twins are not a version of immortality.

There is a wishy washy version of immortality here but it's the same one we have always had, legacy through progeny. Your children were once part of your body, you split them off, they grew into new selfs and you passed on your memories, opinions and stories to them and they carry them forward. Offspring, pictures, movies, stories, histories, crafted materials, art and fame all fall into this psudo immortality of keeping your memory alive, a little bit of you as people like to say. None of these are true immortality where a self does not die.