A reason why they look for 6 mnth avg balance is to determine if the current balance is significantly more than avg. balance . If yes, then it indicates that there are recent credits to account. They want to determine if those credits are legit. Also, they check if there are monthly deductions like loan payments that you are doing. As long as you are transparent and explain the transactions like major credits and any loan re-paypment, you will be fine. Since you got the amount in last one 1 month, you would already be explaining that you got it as gift from your brother.
