It's saddening, but it's true that there's no way you can get your brother's btc anymore. Crypto-assets like btc is unregulated and decentralized, meaning, your brother alone owns it and have the full control over it, unless he have shared its private key to anyone, which you just noted that he didn't. So it'll be forever there in the blockchain; no one will benefit from it nor get it. So may this be a lesson to everybody to secure your crypto-assets before you die. Death is an inevitable and unpredictable thing. If you want your loved ones to benefit from your hard-earned money online, you can entrust your private keys to a reliable member of your family, just in case something happens to you.