my brothers and sisters are still younger than me but I don't know if they knew anything about crypto and wallet, but I have an idea, if it's stupid do tell me.
Your siblings since they are younger than you will respect some boundaries if you set them, it will be a different scenario if you are the younger one, but not so in this situation. Also since they are younger, in most cases you can outsmart them. Even if you write down your seed phrase on a paper, do not be foolish to labeled it "seed phrase" or any name related to cryptocurrency or wallet. You can decide to extend the words by adding some dummy words too, or removing some words too.
That strategy of course is still not the safest because you cannot guarantee that other people will not get to it.