I've noticed some odd behavior when trying to sign in and out of three different Creative Cloud accounts and use each of them for different LR CC photo sets (i.e. business and two family accounts). Since all photos should be synced to the cloud and I've set each not to save local originals, shouldn't they be completely separated and not get any of the photos mixing together? Does LR CC only look at one local database file, or does it change with each unique login?
What's the "odd behaviour" that you're seeing?
If I switch accounts everything behaves as expected, i.e. a separate "catalog" per user is initially created within the same default LRCC library, which then gets used whenever I login with the appropriate credentials.
I seriously doubt Adobe is mixing files among different accounts.
If the files seem mixed, I suggest it's the way you are expecting the system to work and is not caused by Adobe mixing files.
Your account '1' is as different from your account '2' as your accounts are from my accounts.
Since we have no way of knowing how your 3 different accounts are being used, it's impossible for us to offer any meaningful assistance.