Okay...they can help pay half of the offsprings, lifetime cost of living.
I'm no scientist, but I'm pretty sure that even identical twins, while they do share very similar DNA, it is not 100% the same. Identical twins are formed from one fertilized egg, but during the split there can be "copy errors." Theres more to it than that, but I do know that genetically, each twin can inherit a different amount of parts of their parents. For example one twin can be 20% of German decent while the other only inherits 10%. Wild.
That's not how it works but ok