There are identical twins out there whose parents confused one with the other and now they living their life with the name of the other sibling, never noticing because it doesn't make any difference.
We painted their toe nails for the first month but even after about a week could tell them apart pretty easily. Their position in the womb and the birth means they can have quite different head shapes from one another. Also as another comment said, differences in personality are big and start surprisingly early.
My best friend is a mirror twin. His brother cried a lot more as a baby. When they became toddlers his brother complained a lot more. Now as adults, his brother still complains and argues a lot more. I don't understand how they can be genetically identical, have the exact same upbringing, and be so different from the moment of their birth, but they are.
That's not how identical twins are formed. An egg, fertilized from a single sperm, splits into two, creating two people with identical DNA. You're thinking of fraternal twins, where two separate eggs are fertilized by two separate sperm.
It's a lot of stress especially at first, you're thrown in the deep end, but there are really nice moments that I think just increase as they grow older and can play together and interact more.