You have 2 keys, Trustedcoin has 1 key. If you restore you 2FA wallet, you still have the 2 keys and in every transaction you make, Trustedcoin still have the 3rd key to sign your transaction, that is what is most important.
But you question should be how your seed phrase generates the appropriate addresses when you only have 2 keys, it is because your 2fa seed phrase can generate the 3 master public keys which lead to the generation of the appropriate addresses you need for deposit.
You can read this to know more about 2Fa wallet setup on Electrum.
https://electrum.readthedocs.io/en/latest/2fa.htmlIn addition, the third master public key can be derived from your seed, ensuring that your wallet addresses can be restored. In order to restore your wallet from seed, select “wallet with two factor authentication”, as this tells Electrum to use this special variety of seed for restoring your wallet.