I have a friend with a similar problem, AKA chronic renal failure, not on dialysis for the moment, but the doctors keep pushing. Potassium was a real problem at the time, had blood tests once a week
He took MMS on my advice. I must say that at that time I wasn't really sure of what I could say to him, except that biochemically speaking, I couldn't see how this compound could harm him if dosed correctly. He saw it as a last-ditch attempt to avoid the dreaded dialysis.
Three months after beginning to use MMS, his chronic failure receded from terminal to severe, he doses potassium only once a month as he says "to keep the doctor from nagging him too much".
So, it worked in his case, which doesn't mean it is guaranteed to work in your brother's case. The big unknown is the transplant: MMS is supposed to boost your immune system, so there is a possibility (hypothetical) that the leucocytes will turn their attention on the kidney. Additionally, the drugs he takes, most of them immunosuppressors, might interfere with the MMS.
But if he is transplanted and under dialysis, this kidney is probably already going, so I guess the conclusion would be: what has he got to lose?
At least I can tell you that MMS won't interfere with his potassium.
I hope it helped you
