First, I would like to express my condolences on the passing of your brother.
If your brother has income greater than $12,000 (or net Self-Employment income in excess of $400), you should file a return for him. In addition, even if isn't required to file and had withholding reported on a W2 or 1099, you should file in order to receive the withholding as a refund.
Click here for 2018 Filing Requirements.
You can file your Brother's taxes who passed away in September 2018. This will be his final individual tax return. You will need to set up a separate account for your Brother's Tax return.
As you start the TurboTax interview, under the Personal Information section, you should choose "I'm preparing this return for ______ who is deceased". Next, you should enter the date of death. From here you can prepare his return as you normally would.