Well, I have my triple boot setup using APFS Volumes. Now I can boot Monterey, Mojave, and Sequoia all from the internal Fusion drive. The only issue I had was with Open core booting the natively supported Monterey, and messing up SIP and other parameters that should be set differently in a native install over patched. For the time being, I removed open core from the SSD and moved it to the HDD, so it doesn't boot by default, even after a PRAM reset. Monterey, and Mojave don't need it, only Sequoia. Either way, system seems happy now according to SilentKnight.
As far as the same Apple ID issue mentioned above, I gave up on trying to solve it and just don't use iCloud with a secondary install of macOS on the same mac. I never could find a fix other than creating multiple Apple IDs (which I never did.)