From your post, it seems you are indicating that John would have 2 log ins, one for the joint account and one for his sole account? There shouldn't be a need for this at all, when John logs in, he should see any accounts he's on, but not any accounts where he isn't an owner/signer.
Each person must have their own online banking login - no one should be sharing (at least as far as the bank knows) and when that person logs in, any account they are on will show up. If John & Mary have a joint account and individual accounts, when John logs in, the joint and his sole accounts show up, Mary logs in and the joint account and her account show.
As Randy stated, never should accounts being showing under someones log in unless that person is a signer or owner.
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