I understand your worry given the unfortunate progression of your brother's disease. I hope he is coping well.
I agree with Dr Ethan's answer. A general practitioner can check your kidney function (creatinine and the glomerular filtration rate, i.e. your approximate percentage of kidney function) and check for blood and protein leakage in the urine.
I will add to check your blood pressure as well. High blood pressure is a common encounter and one crucial parameter that must be controlled to prevent added damage to the kidneys and prolong the functional life of the kidneys of patients who suffer this disease.
If the general practitioner finds anything abnormal in the screening assessment, hopefully not, he can refer you to a kidney specialist (nephrologist) in the public or private sectors. If everything is ok, hopefully, i would recommend you get those parameters checked yearly, lifelong, in order to detect it on time in case something comes up. At the same time, ensure you follow a healthy lifestyle and healthy weight lifelong to prevent further stress to your kidneys.
Alternatively, you can consult a private specialist of your choice directly, if you are too worried and would like to skip waiting times. He/she will advise you accordingly depending on the findings of your screen.
If many suspected cases, kidney biopsy is recommended for diagnosis confirmation and assess degree of the disease severity, especially if there is significant leakage of protein or the kidney function is subnormal. When the blood pressure is well controlled, the kidney function still normal, minimal leakage of protein and absence of markers of other causes of inflammation in the kidney (what we called a negative nephritic screen), the biopsy can be postponed until something changes; after discussing the pros and cons of watchful waiting (monitor your disease) vs doing the biopsy straight away.
I hope this information is useful. Wishing you the best possible health, Dr Francisco