A Microsoft file hosting and synchronization service.
If I'm understanding correctly you have two Microsoft accounts on your PC and you want to keep OneDrive files locally-available on both accounts. You want to save space but don't want to use the Files On-demand.
Unfortunately, the answer to your question is NO. You can't use the OneDrive folder of another user and still have it actively syncing.
It would be great if there was an account (call it the public OneDrive folder) within the Microsoft 365 Family that all members had equal access to. But sharing folders is the only way to see the family files at this time.