There are two bundles of nerves which run either side of the prostate, and it's almost inevitable that one of them is going to be damaged by surgery to remove the prostate and the associated lymph nodes.
The urinary incontinence can be embarassing, and you learn to keep an eye on where the toilets are when you are out and about. I also keep an empty plastic bottle in the car at all times, and now have a pretty good idea of how long I can hold on for. I also have a couple of pairs of incontinence pants which I rarely use; they're bulky things but are useful occasionally.
For the impotence, well there are some useful little pills around these days which can help ! And having been treated for prostate cancer, I think your brother will find that the doc will issue a normal NHS prescription rather than a private one for them.
A lot of sex is in the head (the one just above the shoulders, not the other one :-) ) and I find that physical stimulation, circumstances and a bit of fantasy helps with getting a full erection, but that it doesn't last as long as it used to - if stimulation stops it goes away fairly quickly :-(
Your brother will find out soon enough how he is affected, and he and his partner may need to make a few changes in that area to keep everyone happy. If it does become a real problem, he should start by seeing his doc for advice and possible referral.