K.,
Are you and your brother close? If you are, and he will listen, one of the things I have done with my almost adult son is take him to the coffee shop, or a restaurant and discuss what I think the problem is and find out if he is interested in working towards solutions. If he is, there are many things that will help. Diet and exercise are excellent for a baseline treatment. Beyond that having daily routines, posting goal reminders, using a timer to stay on task and keeping a daily check off sheet that will keep the important things in front of him will all help a lot. He can use the daily sheet to keep weekly and monthly goals, account spending, to do's, appointments, and his morning, afternoon, and evening daily routines written down. The daily routines are one of the most important things, I think, to help someone with ADHD stay on top of all the little things that tend to slip away. These routines can include simple things like: take meds, eat good breakfast, make bed, shave, 2 minute pick-up, get lunch, back breifcase, etc...
Beyond the things I have mentioned, professional help, like a Life Coach, or a pyschologist can really help. If medication is in order, and for many it really is, a good psychiatrist. Sometimes a General Practitioner will be willing to prescribe the medication, but they are very limited in their understanding of ADHD, the medications, and the comorbid problems that can accompany ADHD like depression, or OCD.
One of the biggest problems that I have faced is the preconceived notion that (especially adults) should be able to control their situation without medication, that ADHD is a behavior issue. It is not. It is a deficiency of chemicals and that can be altered by diet, sunshine, exercise, but it is not a behavior problem. ADHD can have created in your brother some "bad habits" that he will need to re-learn, but if he needs meds, there is no difference between his need for medication and my younger son's need for insulin; they both have a chemical malfunction.
Also, there is a website called Flylady.net. It is actually a woman who helps folks (mostly woman) to keep their homes under control. However, her phylosophy is EXCELLENT for folks with ADHD. You may want to check it out. Her systems can be incorporated to whatever your brother may need to keep it all together.
Good luck to you! Life can be good for him and the family if he is willing to work at it.
M.