There is no difference in terms of cryptographic security, assuming the same program is used to encrypt each volume using identical settings. An important aspect of password reuse is that your security is at most as good as that of the weakest service or software.
If one volume's encryption key is protected by Argon2 and the other is protected with one of the SHA algorithms, then a rational attacker will first try to crack the second volume. They can try more passwords per second with the fast hash algorithm. (They would also try variations on that password; some users think they're clever because they change the last digit of their password or add a "email" or "stackexchange" suffix to it.)
An advantage to separating volumes, perhaps, is that inadvertently leaving one unlocked won't let someone open the other volume. Assuming the encryption software uses unique salts with its key derivation algorithm, even when passwords are reused, then the derived encryption key will not be the same for both volumes. (Also assuming the password itself isn't accessible long after deriving one encryption key from the password, perhaps due to a bug.)
A significant disadvantage to separating volumes is that it you may need to enter the same password twice as often. In theory that doesn't matter, but in practice anyone would be tempted to use a shorter (and thus weaker) password.