I can't support or raise your hopes, but you have to confirm it yourself. It all looks like what nc50lc wrote last, but we've only seen a small portion of the picture.

If I were you, this is what I would do:

• make enough redundant backups so that no data can be lost, especially not the wallet.dat
• import the wallet.dat in a recent version of Bitcoin Core (you may need to use a few intermediate versions, if an import directly to Core v28.0.0 doesn't work
• sync the wallet to a fully synced blockchain to check if there are any UTXOs left
• if you don't or can't believe the outcome, you could use bitcoin-cli getrawtransaction "txid" to check for the existance of every generate (coinbase) transaction in your wallet (this can be painful) --- see bitcoin-cli help getrawtransaction for more details (you should've txindex=1 active to benefit from the transaction index, especially for this command)
  
• you could also check if any of the generated blocks exist in the blockchain (they likely don't, but you should verify yourself and not believe any of us, because we don't have the full details); use bitcoin-cli getblock "blockhash" to check every block your brother mined (the blockhashes are included in the output of bitcoin-cli gettransaction "txid"
  
• you can also search additionally in well known blockexplorers like blockchair.com, mempool.space, bitcoinexplorer.org
• I think it's important to verify success or fail yourself, this will give you confidence to move on, whatever the outcome is
• if it's too much now, because some of your dreams have gone "pooof", take a break and do it later when you feel you've the strength for it

I don't know your programming skills. A lot of it could be automated, but thorough testing is advisable, very thorough testing or very verbose output to check every possible detail.

It will be painful, I'm pretty sure of that. It's totally up to you if you want to walk this path.

I wouldn't delete anything, even when thorough testing and verification resulted in no coins at all. It looks like something went very wrong when your brother mined in those very early days. Not sure if your brother knew if and what went wrong.

Stay strong, life is still beautiful and a joy. Don't ruin your life because of likely no coins from this. (I don't want to sound too pessimistic, sorry.)

I missed the inception of Bitcoin by about only two years. So what? I can't turn back the clock, it is what it is, can't change my fate. Life is still the biggest miracle and I don't complain.