Brief Answer:
Your brother need evaluation.

Detailed Answer:
Hi, Miss XXXX,

Thanks for your question.

After going through your question, I can understand your concern.

Diabetes at the age of 17 years which is not controlled with antidiabtic medicines in maximal dose needs further evaluation. We need to confirm type of diabetes - Type 2 vs Type 1 vs LADA (Latent autoimmune diabetes of adult) vs Secondary diabetes.
Currently he is been treated as Type 2 Diabetes.

There is a need for -
1) Clinical examination -
- height, weight, BMI (Body mass index).
- Signs of insulin resistance.
- Signs of other hormonal disorders.

2) To know the Family history of diabetes.

3) To know the current control of diabetes.
- Fasting and Post prandial blood sugar level.
- HbA1c.

4) To know the complications of diabetes-
- Urine examination for ketones.
- If required arterial blood gas analysis.

5) Other blood tests like-
- Complete blood count.
- Liver function tests.
- Kidney function test.
- T3, T4, TSH.

With the information provided in question, it will be difficult to suggest any changes in current medicines without knowing current Blood sugar status and clinical examination.
Only I can say insulin may be the option for better blood sugar control which can be used any type of diabetes safely, but it should be taken in consultation with your doctor.

Hope this may help you.

I will be happy to answer your follow up question, if any.

Regards,
Dr. Abhay Mali.
Diabetologist.

---