What is the expiation for stealing money from one's father and employer, and how can one repent and restore rights without causing them embarrassment, knowing that they are unaware of the matter and the thief has already left his job?

You must repent to Allah and return what you took to each of them, because "what the hand has taken, it must return until it is paid back." If you are unsure about the exact amount, err on the side of caution to clear your conscience. To avoid embarrassment, you can use allusive language when returning their rights to them without admitting to embezzlement or theft, for "in allusive speech there is room to avoid lying."