The aim is to create 3 packages of cryptographically secure backups where the funds cannot be recovered from any single package, but can be recovered with the combination of any two.
Can be thought of as a physical 2-of-3 multisig solution.
A well proven way to generate random 12 word list is to create a new wallet seed in Electrum Wallet.
To use Electrum boot Tails (ideally offline) or download and verify the wallet on an existing system.
Follow steps 1-5 in this guide to get the seed. The wallet file is not needed, only write down the words and store accordingly. The 12 words are to be used as a passphrase, encryption passphrase, cypher phrase or wallet unlock password. Do not reuse passphrases for more than one purpose and label the backups clearly.