Please accept my condolences on the death of your brother.
Do you have your brother's Apple account password, if not can you try to reset it? If you can get into his account, then you can probably try to adopt his account (change account email and password, credit card etc), although then you wouldn't be able to use any purchases that you have made on your account. There was some news in the media last year when Bruce Willis found that he could not leave his iTunes content to his daughters when he dies. I seem to recall a subsequent change in the rules but it might need some searching of Apple's T&Cs to find it. Sadly you cannot use multiple accounts on iOS devices. I'd be sure of the rules before going to Apple for any help in merging accounts as they might insist on cancelling your brother's account. If its too painful for you to do, maybe a friend can help?
I bought an iPad for my father to use in hospital last year. When he died on New Year's Eve, it came back to me but I gave it to a friend. That required re-setting the device which was very upsetting, even though he only ended up using it for a couple of weeks, so I can imagine how you are feeling about losing that link to your brother.