This is what I know...kidneys are responsible for removing excess potassium from the blood. Diseased kidneys will not be able to do that well, which results in too much potassium in the blood. Our hearts are regulated by potassium, along with other things. So, I am sure they checked her levels and found them too high, which could potentially cause heart and other nervous system issues.
I've been interested in this subject as well, though I haven't really been able to find any information as to wether 801010 is good for someone with kidney disease or not. My Dad also has kidney disease, and he too takes potassium blockers. The really irritating part is they tell him to eat lots and lots of meat, which is of course a big contributer of kidney disease in the first place. (at least they did while he was on peritoneal, I'm not sure if they still recommend it since he's switched to hemo)
I'm very sorry about your Mom and your Uncles; I know it's tough because I've seen my Dad deal with it for five years now.