It's your parents money, so you must agree with their choices. If you want to invest in Bitcoin, then only use your own money that you collect or receive from anywhere.
Similar like you don't like a or few things in your parents house, you should leave your parents house and start to rent a house. As long as you're still eat from your parents, you have no right to control anything.
Imagine you're at a casino with a friend. Your friend is hesitant to gamble, but you convince them to put some money down on a roulette bet. The bet loses, and your friend is angry at you for convincing them to gamble.
I don't see any reason why you can compare Bitcoin with gambling when Bitcoin price is keep increasing despite there's ups and downs while gambling is definitely 99% you will lose your money.