the first thing you have to nail is to provide proof of bitcoin itself. only when they already believe, teach them slowly. because without proof parents will not believe and want to accept and even learn what bitcoin is and how to get income from bitcoin.
You can prove the existence of bitcoin, but I think it will be more difficult to convince them that you can make good money on it
Not even true.
Convincing then that you could make money on it is very easy, just show them the funds and the transaction you have and they would believe you in just seconds. Old people might not be into advance technology stuff but they are not that dumb when you have proofs to prove that Bitcoin do really exist and it could change your future by believing on its capability that beats the fiat system.