Hi! I think your brother is going to need some medical advice to get to be dry. You might start with
http://www.spinal-injury.net/bladder-management-sci.htm which is a fact sheet that ought to help.
The thing is, does he have to cath or could he use a sheath and a leg bag. If his bladder empties and doesn't leave much residual urine, this would be a good way of dealing with leaks. Howver, it does involve a leg bag and some people apparently don't like them - I have one on now and I can't feel it so it doesn't bother me.
Another simple solution might be for the doctor to give him a drug to dampen down the bladder giving more time to use a cath.
Finally there is the solution I have. I have a catheter inserted into my abdomen (initially under anaesthetic) called a supra-pubic catheter (SPC) which drains the bladder well and is much better for infections that the intermittant catherisation your brother is using now. As long as one keeps drinking, the catheter can sty in place fro 10- 12 weeks and it is asim0ple job to change and you can learn to do it yourself. The only serious snag is the need to keep the lag bag attached all the time and connect a night bag to it for over night.
You are going to have to talk to the doctor to work out what would work out best thig based on the bladder's function. Come back for more advice though.