All remittances to Pakistan come via State Bank and then come to your bank. All you need is to tell your brother to mention the purpose of the payment. Once the payment comes to your account; tell your bank to issue you a Proceeds Realization Certificate or PRC (its a document that basically says that the bank has received funds from so and so, the amount, purpose, dates etc AND says that the transaction was reported to State Bank). The first time, you'll need to submit a written request, afterwards they will most likely get you the PRC when you authorise them over email.
At the end of the year, you declare the full collective amount received over the year into your income tax statement.
Also, if your brother wants to save money on transfers, tell him to use transferwise. You can take a look at the article here: https://tech-vise.com/transferwise-best-international-money-transfer-service/
Ive been using the service for over a year now. Its very fast and the transaction will come directly into your PKR account. The service can be used for personal payments only.