Essentially so ( monozygotic twins ) as they are the result of zygotic splitting in the womb.
Still development can alter the genome somewhat so that these twins are close to but not quite clones.
Do twins have the same dna?
It depends upon whether the twins are monozygotic or dizygotic. If they are monozygotic, then many genes are going to be identical in the twins. But in case of dizygotic twins, the possibility of identical genes will not be more frequent like monozygotic twins.
This thing is responsible for many genetic disorders like autism. That's why genes responsible for autism are found in siblings.
yes some do.
Another older question, but here's some interesting information on a theoretical situation where one of two twins with identical DNA commits a crime, but leaves nothing besides his DNA at the scene: