I cannot access the hidden wallet.... but is there still a way to access the coins, if I have the seed, but not the passphrase?
No. You require both the seed phrase and the passphrase to access the hidden wallet and the coins inside. If you lose the passphrase, then you cannot access the coins in the hidden wallet, even if you still have the seed phrase.
Passphrases are not stored anywhere, you need to remember it.
Bad idea. You should back it up on paper, separately to your seed phrase.