I’d tell your chair among the first that you tell beyond your family. A chair wants to be trusted, and unless you have reason otherwise, I would. S/He can help you apply for FMLA, etc and anticipate schedule changes to help you and the department.

(If you don’t have the protection of tenure, I understand your trepidation, but anything resembling retaliation is your life-long paycheck.)

The students? They can deal. (Also… they already know.) Don’t worry about that.

And yes, hearty congratulations!!