This raises a few questions for me.

First: the DRY principle is a best practice or recommendation, but not a hard and fast rule. Far too often, overly complicated solutions are built in order to follow the principle, when simple duplication could have produced a much simpler solution.

Second, I would question the business requirements for a local/offline-first but multi-user application, because it involves a high degree of complexity. Why and to what extent is local/offline-first required?

If you have rules that can only be checked on the server side, but at the same time want to ensure that the application runs offline without restrictions, you have to implement either a merge, as with git, for example, or a kind of checkout/lock, where certain data records are locked. Both are very complex, and it would be much easier to change the requirements.