Regarding Mnemonic Code words and salt key
Third Parties should extend your mnemonic phrase with your passphrase else they will get a different wallet with different addresses.

Electrum and some other wallets call the passphrase a "seed extension" or "mnemonic extension".

Third parties should have an option to extend mnemonic phrase with your passphrase, It's a weird idea to possibly have enough money to purchase the entire building just sitting on a sheet of paper without any protection. For this reason, many wallets make it possible to encrypt a mnemonic phrase with a password.

Take a look at this open-source project, you can import play around with any mnemonic phrase and extend it with your passphrase and see the changes