Sibling asked for help stacking BTC

Hi all. What would you recommend please. Sibling asked if I can help with stacking sats. They will send me desired amount each month. They have little to no knowledge on good wallet practices, seed phrase keeping, etc. How to keep my own btc separate from theirs? I will eventually explain how wallets work, what seed phrase is and all other important stuff, but what would be good way to start this before they have enough knowledge to do this on their own?