A parent may have helped create you, but they have absolutely no right to be emotionally and mentally absent with you, THEN demand that YOU teat them better than they've treated you!!!
You are no doubt hurting from the emotional abandonment by your mum and DB, but that doesn't mean you should run away from the pain of facing up to this. It will be hard, but it will most likely allow you to move on quicker than you would if you kept running away from it all.
Think of it logically and objectively. You have a number of anxiety/emotional/mental problems that need unpicking/untangling and sorting, bit by bit. They will always be with you until you make the emotional and mental effort to solve them, as much as you can. The worst thing you can do is to NOT face these problems head on. You'll probably feel a whole range of emotions, from sadness, to anger, but these are absolutely normal, considering your circumstances.
YOU, have every right to be treated with respect, and if your mum/DB are not doing that, then call them up on their behaviour toward you. Should they become angry that you dared expose their behaviour, you can simply tell them that "If you hadn't acted like that in the first place, there'd be no behaviour to call you out on". This simply reiterates that it is THEIR BEHAVIOUR that is the problem, and that you are simply reacting to their actions toward you.
Last but not least, please do not be afraid of conflict with them. Refusing to call them out is allowing their actions toward you to continue. If they get angry/annoyed about you doing that, then they're just angry that their horrid behaviour is being exposed, and that will not make them look good.
You didn't make your mum or brother do those things. Their actions are their choice. You didn't ask to be verbally/physically/mentally/emotionally abused. They CHOSE to engage in those actions themselves. You don't have to put up with it any more, and if that means you go LC/NC, then you should do that to protect yourself and your DC.
BTW, the only regret you should really have about this situation is not doing what is best to protect your DC from this. These people are toxic, and you'd be best keeping them safe from this kind of behaviour, as much as you can.
If you mum/DB decide to come over to see you can say "Sorry mum/DB, I'm on my way out now", if they show up unannounced, or another phrase that is repeatable ad nauseum is "I'm sorry, that doesn't work for me". The last comment is something that is a non-committal response to a person you don't want too much contact with.