If you selected Multisig Shield during the setup process, your Liquid wallet in Blockstream Green uses a 2-of-2 multisig model, similar to your Bitcoin wallet.
Sending a transaction from your Liquid wallet requires a signature from both your device (protected by PIN) and the Blockstream Green server (protected by 2FA).
Currently, Blockstream Green does not support the creation of 2-of-3 accounts on Liquid wallet. This feature is only available on Bitcoin wallets at present.