@kristrose I remember you from your own thread. It was horrifying abuse.
Of course his mum won't intervene. Where do you think he learnt to behave like this?
Social services won't have any reason to think you're a bad mum if you've protected your children from him. At the moment though you're still teaching them that this is normal behaviour.
You've described how appalled you would be if your son was the one doing this. But can't you see that you're setting your children up to repeat this pattern if you don't take the leap of leaving? If you take them out of this environment you won't have to worry about them repeating this in their own lives. Staying is teaching them this is acceptable and normal.
The mother of your abuser is not the place to look for support. You've described that she won't do anything he doesn't like, so why do you think she'd support you over him?
You had good advice on your own thread. Places that will provide actual support were named.
I do understand how hard leaving is, I've been there, but at a certain point you have to decide to break out of the cycle and jump. I know it's hard when they're making your head spin, but your head won't stop spinning until you get out.
You said you didn't have your father around, so you want them to. Can I offer you my perspective having been the child growing up with the abusive father? I still wish on a regular basis that my mum had been brave enough to leave him and protect us. I still hurt that she didn't love us enough to do that. The abuse I witnessed and endured from my father set me up for even worse abuse as an adult and nearly destroyed my life.
Having no father is better than having an abusive father. If you want them to have positive role models, then find positive influences. They don't have to be biologically related. But this man is a destructive influence. They won't thank you for staying. They will if you leave.
If you're pissed off about Eminem, can't you use that anger as your final push to get you to change this situation? You can be the one to take charge of your life. Leave, go to the concern, start your new life with a bang. Nobody's going to sweep in and save you, you need to be - and can be - your own rescuer.