My brother graduated and lives in my house.

Since your brother/kloc-is 0/6 years old and you are his own sister, you should take care of him anyway. You must discipline him like a mother and don't let him form any bad habits. Even if you spoil him, your daughter will see it later. How you will tolerate him after imitating him is tantamount to hurting him. Of course, don't set too high a constraint, so his heart will be more unbearable and he will be more rebellious when he is sixteen or seventeen. If you don't manage it well at this time, it will be more difficult to manage it in the future.