Welcome to HCM,
Your brother is having renal failure
and nausea and vomiting is main clinical feature of this as wate products accumulates in blood,but also there could be acute stomach problem like gastritis on top of renal failure which precipitated vomiting,is he hypertensive or having some cardiac problem and taking drug which may add to the cause of vomiting.
Your doctor is right please do not take medicines of which contents are not well known and may have nephrotoxic ingredients.
There are very good drugs to control vomiting please take prescription and if it is too much get hospitalize so that injections can be given to control his condition.
Renal failure treatment depends on cause and consult Nephrologist
take Low protein diet
and low potassium diet and fluid as directed by your doctor,if reversible cause is there like dehydration
and infection usually it improves kidney function and creatinine
level will come normal but if it is due to kidney damage then if renal function gradually deteriorates Hemodilysis may be required in late stages.
Just take very good care