My dad idled a car in the garage for five minutes, could the carbon monoxide seep into my house?

Oh dear you really are a hypochondriac aren't you! So the car exhaust was going outside the house (as the garage door was open) You really think that you were poisoned by an engine running in an environment where it was open to the outside air. There will be no seepage as any carbon monoxide is going to be distributed amongst open air and will not even make it to your house! If the CO did rise to fatal levels you would already be dead & not worrying about it so breath deeply stop being so stupid & calm down!