This question keeps popping up.
Here is the answer:
Obviously, fraternal twins are just like any other siblings:
Blood types can vary.
But how about identical twins?
We do know for example that identical twins have different fingerprints.
Monozygotic twins are genetically identical unless there has been a mutation in development. and they are almost always the same gender. (On extremely rare occasions. an original XXY zygote may form monozygotic boy/girl twins by dropping the Y chromosome for one twin and the extra X chromosome for the other.) Monozygotic twins generally look alike. although sometimes they appear as mirror images of each other. Identical twins will also share the same blood type, eye and hair colour.