I think these would be fratenal twins. Identical twins are of the same sex because they start their life from a single zygote and then the early embryo splits in two parts, each part then develops as an organism. Fratenal twins on the other hand, can be of different sex because they arise from two different fertilized eggs. Fratenal twins are siblings who happen to share the womb. Identical twins are monozygotic, the zygote formed by fertilization of an egg by a sperm. thus identical twins inherit the same chromosomes and genes; which means they are genetically absolutely identical.
