Yeah, a person will know the value of the gift if they really know what the gifts are. If they don't know and we don't explain or teach them about the gifts, this will not really good. KNowledge about crypto for some people is still new and some of them may still not be able to understand or accept Bitcoin or other cryptos. That is why, before or after giving Bitcoin as a gift, it very needs to give them certain lessons about what Bitcoin is, its value, the advantages, and others. Because, if they are not, the person who gets the gifts may think it better to sell the BTC directly, so they can buy some other goods that they are really willing to. Moreover some women may not really love this because they only want to show something new from their boyfriedn to their friends.
Because this is more personal, I think OP can have more control over the gifts given, so that the recipient, in this case his sister, can do the same thing as the initial bitcoin investment. However, if this gift is resold, it is certain that OP will not succeed in educating his younger siblings to develop themselves in investing. While others are very open to bitcoin adoption and investment.
Today many communities and individuals have seen how great bitcoin is, so they need to take a role in investing in bitcoin, and I believe the OP understands the concept of investing more, so it's not difficult to teach this to his brother.