Your younger siblings are learning your standards whether you’re teaching them or not.

Younger siblings learn from behaviour, not instruction. They watch how you speak to your parents, how you handle losing, what you do with a boring job, and they copy the version you perform rather than the one you describe. None of that waits for your permission. You are an example by position.

Pick the habit you would least like to see repeated and work on that one this week. Then let them see you do something ordinary properly: homework at the table, dishes done unasked. They will remember what you did long after they forget what you told them.