"Oh, don't get me wrong, they fight. An instant sibling from the start to irritate, poke, and run off with their favourite toy, or whip a biscuit from the others hand. This is 5% of the time. And honestly, it's quite funny. Seeing one bolt down the hallway, waving a biscuit, victorious as the other zips past a few seconds after, to get their biscuit back."
This reminds me of the stories told by my goddaughter's mum - my goddaughter is one of twins - my friend already had three aged 5 and under when the twins arrived - and my goddaughter was a faster learner than her brother.
When she could crawl, and he couldn't, she'd crawl down to his end of the cot, steal his dummy, and crawl away with it. She learned to walk before he did, so she'd nick his toys and walk off - sadly for her, he could crawl faster than she could walk, so he'd zip off after her, pull her down by the seat of her trousers, and get his toy back.
They are grown up now and are still the best of friends.