I'll mirror what someone else said, have they actually sequenced them? Clearly a lot of changes happened at a very early state, mutations, so why should we expect their genetic makeup to be identical?
In animals and human chimeras, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, and subtle variations in form (phenotype).
For example, in 2002, news outlets reported the story of a woman named Karen Keegan, who needed a kidney transplant and underwent genetic testing along with her family, to see if a family member could donate one to her. But the tests suggested that genetically, Keegan could not be the mother of her sons. The mystery was solved when doctors discovered that Keegan was a chimera—she had a different set of DNA in her blood cells compared to the other tissues in her body.
