First of all, you can file the application(s) for disability insurance and/or supplemental security income without the services of an attorney. Most people choose an attorney when they are denied and decide to appeal to get a hearing before an Administrative Law Judge (ALJ).
If you work while awaiting a decision, the decisional direction depends on how much you are earning. SSA counts your gross wages (assuming you aren’t self employed) and compares that amount to the standard for “substantial gainful activity”, which is presently $1010 per month. Of course, just keeping your wages to $1010 or less per month doesn’t mean you lack the capacity to earn more than that.
The disability process can be arduous because you must establish that your physical and/or mental impairments prevent you from performing any work available in significant numbers in the national economy. You may live in an area where there are few jobs, but SSA doesn’t really care about that. At age 50, if you can establish that you are capable of no more than sedentary work (lift/carry 10 pounds or less; stand/walk 2 hrs per day; sit 6 hrs per day) AND you are unable to perform past relevant work or work where you can easily transfer your skills, you can be approved. At age 55, the exertional limit climbs to light work (lift/carry 20 pounds; stand/walk 6 hours per day; sit 2 hours per day), plus everything else that the age 50s need.
Various jurisdictions have reputations for having tougher judges, and, Racetrackreject, I’m afraid that TX is one of them. However, if your brother is truly as limited as you suggest, he would benefit from the services of a disability advocate or lawyer who can obtain the information needed to prove his limitations. [And I generally recommend that you avoid one of the biggest commercial advertisers, as those attorneys don’t always prepare the case well. A good local attorney who is well aware of the foibles of the local ALJs is your best bet.]
If you have specific questions, please PM me.