I can't see much logic in you're perspective as well. Just blind belief and wishful thinking in regards to scientism.

I know that that your perspective may sound logical to you, but it isn't True.

I haven't considered the subject you're offering yet, but I'll give it a go.

Siamese twins is just a simple malformation in nature. It's something natural, happens all the time.
The thing is that since they both have their own operating centers (heads) they can both form their own personality.
That is normal. But it also happens that one person has two different, distinct personalities. That's also normal. You can at all time act as whoever you want to act. There's no restriction to that. One individual might create two, or even more personalities for the different things they do in life. And they always switch between those personalities. We ALL do this to different extents. But there are these multi-personality disorder individuals who create such different personalities, that it's like they become someone else when they embody each of the personalities.
In you Mind is Everything. Your Imagination is capable of Everything. You can choose to act as any other personality withing this world. That has died, that is alive, or even that doesn't exist yet. But that posibility is still within the range of your Imagination.

Please start questioning these "scientismical" logic mind traps.