Normally pgp. But if they're not capable of having a seed themselves, then pgp will be complicated to set up.
Is my assumtion right that you should take the encrypted file to an offline device (e.g. Tails) to encrypt it there and use the seed from there? I would not encrypt the seed on a device connected to the internet.
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That's right, the most I can manage is having them put the seed in a wallet app and destroy it for safety, I'll be keeping the backups.
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