If someone decides to have children one day he or she should know that inheritance works in a very complicated and mysterious way. Every parent has a full set of exactly 46 chromosomes. But each parent can pass only 23 chromosomes to their child. Exactly which 23 chromosomes are passed is entirely a mystery of nature and is usually at random. Only identical twins are unique because they receive exactly the same 23 chromosomes from their parents.
It’s good to know that if a set of identical twin females get married to a set of identical twin males and eventually had children on their own the family relations would be somewhat bizarre. Their children would ultimately be genetic siblings but not genetic cousins. They will have the same DNA coding inherited by their parents which would mean that genetically they are all the same.