How are twin babies form?

 twins are produced from a single egg by the separation of early blastomers resulting from the first zygotic cleavage. As a result , the young ones formed will have the same gentic make up and are thus called identical twins

if the twins were born fraternal, then they would have developed from 2 eggs. This happens when 2 eggs are releasd at the same tym and get fertilized by 2 separate sperms. Hence, the young ones developed will have separate genes .