Some policies will disable your Yubikey/U2F key if it goes unused for N days. Usually low enough that it's annoying to keep a backup key.

We've used https://rsc.io/2fa to share TOTP keys between multiple individuals. We store the secret key in a shared password store that's also behind a separate 2FA login.

For U2F, check out https://github.com/github/SoftU2F