There’s a pretty famous case of a child who died from apparent antifreeze poisoning. He had been vomiting and had trouble breathing, and doctors found high levels of ethylene glycol in his blood. A couple of years later, his brother started having the same symptoms. Two brothers, sick in the same way, it would seem likely that they were both poisoned with antifreeze.
But, at the time the younger brother was showing symptoms, his mother was in prison for the murder of the older brother. It was determined that
Patricia Stallings’s sons weren’t sick because they were abused in the same way, they were sick because they had the same disease.
Until more facts come out, I’m open to the idea that there could be some unknown other factor that the twins have in common, or even that their injuries were unrelated.