Database structure

I have a Realm database with some items ( “Item”) , I need to synchronize only some of them depending on a boolean property value ( “offline” ). Those items are only visible to the user that has created them. for some of those items I need to synchronize only certain properties, how can I do this? Do I need to split objects?

Some items can be shared between multiple users (20-25), what is the best implementation to do this?

Is Query-based sync going to be discontinued?