Twin cousins explain how they are also brothers

What are identical and fraternal twins? 

Let’s start with the basics of how embryos form to understand the mechanics of where twins come from.  During ovulation, one or more eggs are released. When an egg is fertilized by sperm, it’s called a zygote. The zygote quickly starts growing into a small cluster of cells that travels from the fallopian tube and implants in the uterus. It continues to grow and begins to form a placenta, which provides nutrients to the developing embryo.