- https://iancoleman.io/bip39/
Paste the seed phrase he had and then go to the derivation path then client and put it to Multibit HD.
Copy the xPub or extended public key and paste it to this link below repeat the process to other clients until you find used addresses on the xPub scanner below.
- https://blockpath.com/wallets/local/101?action=appxpub
Once the tool found some used addresses focus on that client for the recovery process.
For safety purposes, you can run the BIP39 tool offline if you don't want to expose the seed phrase online.
You can still get the compiled binaries and source for mulibit here: https://github.com/Multibit-Legacy/multibit-hd/releases
And then see if you can import the seed and what addresses it gives you and work from there.
The other possibility is that it was not BTC but some alt.
-Dave