maybe look into local merchants/retailers that accept bitcoin in their local town. and along with the book send them invitation to make a btc address and you will send them enough for a coffee, pizza, doughnut or cake at the local store to buy.
That would be a great approach but you possibly don't know (I didn't share here) that cryptocurrency is illegal here. So, no chance. I would be more than happy to have them such a gift.
Most important question is, do they have an interest in bitcoin the same as you? If yes, there is nothing wrong with whatever approach you will do and besides, they are your relatives and they understand you more than anyone if they witnessed your success using this bitcoin. But if they are not into bitcoin, I doubt if they appreciate that idea.
If they had an interest in bitcoin, they would learn it through the internet. I'm trying to create awareness or make them known with cryptocurrency. They are a lot of people who don't know what cryptocurrency is or they don't have a good impression of bitcoin. I want to make them known, I want to change their perspective.