I can’t see you ever got an answer to this. Reading what you’ve said, no I don’t think you have let him down. You took the right (albeit harder) option for the long run rather than the easy one (accepting your violent brother back into your life so everyone was happy with your decision). That must have been hard, especially with your mum, sister cutting you off and now your son missing his extended family. It was a tough decision, but you also matter too. I don’t think you made then wrong decision.