But how is that any different than identical twins? One egg, one sperm, one blastocyst – oops! Now two blastocysts! Two embryos, two fetuses, two babies, two unique, yet genetically identical, people.
Me, I don’t think the soul enters the body at conception, so it’s not a brain teaser for me. There’s two fetuses and somewhere along the line, a soul will inhabit each one, just like any singleton fetus. (I think, based on observations of micropreemies, that the soul goes in and out for quite a while until it decides to stay in the body - rather the reverse of what I’ve observed in slowly dying people, where the soul flits in and out for longer periods of time until it just doesn’t come back.)