Great that they get along wonderfully. I just talked to my Vet a few days ago and she agreed with me that it's often easier to bring together male cats and kittens than female cats and kittens.
Axel (the tux) was her only cat. She had another, but he passed away from kidney failure a few years ago. And she had a white, deaf cat that lived to be almost 20. She tried adopting a 9 year old female cat, but she was like Chloe -- wanted to be the only cat, so she was brought back. Skittles is 6 weeks old and my sister is fostering him to adopt because his mother stopped nursing at the shelter. These two hit off right away.