Female Chestnut-backed Chickadee busy building nest

The female chickadee started building her nest last Saturday, 2/17/2018. But she’s working hard at it today. I’ve been watching her fly down to the neighbor’s yard, gather a good billfull of redwood bark fur, and head back to the nestbox on my balcony to add it to the growing nest.

Chickadee Family

This looks like a Chickadee family but I’m not sure. Definitely a fledgling and 2 adults but the one above looks like a Chestnut-backed and the adult below looks like a Black-capped, the baby looks a bit more like a Chestnut-backed too. Do they cross breed?

Chestnut-backed Chickadee eggs in nest box

Juvenile Chestnut-backed chickadee