Who actually creates the new chain and how?
Anyone can create a chain split and hard fork. You do so by releasing software which has incompatible consensus rules with the current consensus rules.
Is this just the development community? How can a minority of the devs create a new coin
It is not "the development community" but rather a specific group of developers. As I said, anyone can do whatever they want; it's an open source project, they can fork the source code and change it.
if consensus is required to change the protocol?
Consensus is not required to make a fork and an altcoin. Consensus is required to make a fork and have everyone agree that that fork is still called Bitcoin.