Okay guys I have an update!

So on Guarda, me and my partner checked each of our individual Guarda wallets. We checked the private key for the address.
We both have different private keys, which was expected, BUT my guarda ALSO has a mnemonic phrase (12 words), whereas my partner does not. I assume this is because I initially created the wallet and my friend joined? Does that mean that mnemonic is the master key or something?