Your brother sounds like my sister. Except that she has managed to hold onto jobs for years at a time, before something happens, either her being late to job and or conflict with boss. Unfortunately she is now in her 50's and only has essentially just above entry level type mostly service type experience. And they are going to hire a young peppy person over a 50 year old for that type of job.
I don't know if it is ADHD, or possibly some other type of issue (there is actually a disorder called oppositional disorder, also bipolar II, depression, etc) that is hampering him, because his job history is not normal. Most people can suck it up to keep even a crappy job, boss situation. He needs to figure out a long term situation for whatever is going on, by maybe seeing someone, getting on medication, whatever. He needs to learn how to be an adult, and that is taking care of yourself and not expecting someone else to do it.
But I feel for you. It is NEVER easy. I have 2 kids and am now divorced, no financial help from Ex. I moved many states away from my original family, never asked for assistance after graduating college to underline, I have my own life, my own priorities and responsibilities. I don't ask anything of you, do not expect anything from me. But I still get sucked in sometimes.
One thing you have to realize, unless it is a once in a blue moon situation, you giving money to bail out your brother is not helping. It is enabling. You can still be his brother, give advice, be there for him in other ways, take him to a career placement center, research stuff. But do NOT help financially. Even if your Mom is still enabling you need to get out of that cycle. Honestly it would be best if Mom did as well, have an intervention. It's worth talking to and maybe giving your mom some information about how she is helping is not helping him long term. She might see the light, she might not, but that's her road, not yours.
