Just because they look alike ...
Watch out before you call super-gymnasts Paul and Morgan Hamm identical twins. There's some disagreement here.
Their parents say they are fraternal, but that it is murky because they were born with separate sacs in a shared placenta. But Slate writer Josh Levin quotes a doctor as saying that 99.999 percent of these twins are identical.
So what should you go with? Levin decides to go with science and, truth be told, that's probably the right answer. But unless it's pertinent to your story, take out the modifier and just go with "twins."