I convinced my parents to buy bitcoin

I bought Bitcoin for my parents. I managed to convince them to buy Bitcoin, but they didn't want to be involved in the purchase process, so they transferred the money to me, and I bought it through my exchange account and am keeping it for them in a cold wallet. Now I'm wondering if there might be any problems if they want to sell it in 5 or 7 years (for example). I'm from Germany, and profits are tax-free after one year. So, what if it's a six-figure sum? Does anyone have experience with this?