How to help kids change bad behavior?

My boyfriend and I live together. I have a 14 year old son that goes between mine and his dads house. He is very well behaved, and listens to me.

My boyfriend has 4 boys that are 3, 5, 6, and 10. They haven’t had any contact with their mom for over 3 months because she chooses substance abuse and to stay with a boyfriend that is abusive to her and the kids. Until cps was involved though my boyfriend and his ex had split custody so the kids were exposed to this abusive and aggressive behavior.

I need help figuring what to do to help change their bad behavior. I stay home taking care of them while he works. I know boys are more rough, but they hit and spit on one another, break one another’s toys, refuse to go to bed at night, ect. I have gotten them on a bedtime routine of watching a movie with popcorn before bed, then brush teeth, then I read to them for 30-50 minutes, depending on if they’re being quiet and calm.

For discipline I refuse to spank, I never did it with my children, and will never lay a hand on others kids like that. Hugs and cuddles yes, spanking no. I have tried time outs, which most other than the 10 year old will not stand in timeout. I have tried taking away some of their toys, which has caused the 3 year old to call me a Mother F****R, and he likes flipping everyone off.

They’re not allowed to watch YouTube any longer, and screen time in general has been very limited as well. When I do allow them to watch a show, I have it be something that is age appropriate and educational.

They are very good kids when they’re behaving, however when they’re bad, they go crazy. The 10 year old has been caught punching, hitting, scratching, and otherwise harming the younger siblings, always claiming when caught that “it was an accident”.

The 6 year old will scream and throw temper tantrums, and throw himself on the ground.

The 5 year old is probably the best behaved, however will still break his brother’s toys when upset with them. As well as throw tantrums when told to do something he doesn’t want to do.

The 3 year old refuses to take naps, breaks anything, gets into everything in the kitchen and flings it all over the kitchen, calls everyone bad names, cusses, flips everyone off, I could go on.

Any advice is greatly appreciated. They are all great kids, and even when they’re misbehaving i let them know i love them still, and I’m not going anywhere