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