What do you think about me using my stepmom cheating on my dad as leverage?
That doesn't sound like a good idea. What does using the cheating as leverage accomplish?
Because I want to make sure my brothers don't become as stupid as my stepmom
Wanting to keep your brothers safe from your stepmothers bad influence is fine but you shouldn't be using information in order to manipulate her. If anything you should tell your dad about it and be honest and see how he handles the situation.
It's fine, you don't get it. I like my brothers and would do anything to make sure they are safe.
It's great that you want to protect your brothers, however you should not do so by manipulating them into seeing your stepmom in a negative light.