My girlfriend and I have been together 3 yrs, our son is 1. She had children already ages 12, 8, and 5(current ages) They have always caused issues with their behavior,  we moved in together about 2 months ago, and its been bad since day 1. I've been asked to be disciplinarian, but when I do it causes problems. It's fine for her to say I'm gonna get mad and come in room to scare children as a threat but as soon as I say anything or even raise my voice I'm the bad guy. When I bring subject up, its immediately met as saying she's a bad a parent which is not the case.