If you are saying that (according to astrology) they should have identical lives because they are born at the same time, then that would apply to any twins, genetic similarity having nothing to do with it.
And in any case, twins, identical or not , are not born at exactly the same time. I'd expect astrologists (I myself not being familiar with any of it) to say that their lives would follow similar courses with some differences - which would usually be a correct prediction. Also they are not the same person, whatever predictions or analysis provided, assuming it is the same, would be understood differently by each.