Gideon55555555 I have siblings as well, so I know it can be tricky keeping them off your games.
If you play on PC/Steam, I'd suggest having your own Windows user account login so your siblings cannot just play on your account, (as for Xbox/PlayStation, there should be a way to password lock those accounts as well). However, if you are a Nintendo Switch player, you are sadly out of luck as there isn't a way to lock an account on the Switch's platform.
Hopefully everyone in your household has their own account.