It doesn’t work anymore

I'm feeling lost and overwhelmed with managing my 8-year-old son's behavior at home. I also have a 7-year-old daughter and an 11-month-old baby. My son generally understands and performs well in public settings, receiving compliments for his manners and behavior. However, at home, he struggles with accepting "no" as an answer and managing his emotions.

For instance, the other night, he asked for a bath around 7 PM while we were playing games as a family. I initially agreed, but later, around 9 PM, I was too tired due to being up all night with my youngest. I explained to him that I needed to get to bed on time and suggested he take a shower instead. This led to a major meltdown from him, including losing instructional control and refusing to accept consequences.

The next day, he continued to struggle with accepting consequences and engaged in a power struggle with me. This included disagreements with his sister, inappropriate behavior like throwing away her pencil during school time, and not starting his school work until late afternoon.

What concerns me deeply is his behavior when I'm not looking. For example, when I left to use the restroom, my daughter started doing front flips off the couch, and he maliciously moved a trash can where her head would land. This deliberate act of cruelty, which we observed on our house cameras, is troubling and shows a level of behavior that I don't know how to address with the rule of three or other techniques. I have observed it on the cameras multiple times of him tripping her, throwing her, and throwing things at her. If these situations happen I have them practice each situation three times. I mention our family vision, and our mission, and on the surface it seems like there is compliance, but when I leave the room again this is what the camera shows.

Despite using scripts and techniques to manage the situation calmly, he persisted in resisting consequences and escalating conflicts. This behavior isn't isolated; he exhibits similar outbursts about twice a week, leading to disruptive and homebound days for our family. While techniques like the rule of three and scripted responses initially showed promise, they seem ineffective once he receives a consequence or doesn't get his way. This has left me feeling defeated, especially as previous programs and strategies have only provided short-term relief before the issues resurface. What do you do when it is just not working anymore?