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You can, but it’s weird
1. Setup your Trezor and give your sister the seed-menmonic (weird)
2. Then add a passphrase that will be your sister (aka “sister”)
3. Then add a passphrase that will be you (aka “brother”)
Now to access the “brother” account, just type “brother” in for the hidden wallet. To access the “sister” account, just type “sister” in for the hidden wallet.
Only one physical device is available so you two would need to share the physical device, and if you use trivial passphrases like “brother / sister” then each of you will be able to access the other’s funds (weird).