Use iCloud + Core Data. Mark all relations optional, store objects IDs in data-folders-linker, and enforce them programmatically. You can do it because your db is simple enough.
iOS7 even deletes orphaned objects with non-optional parents and cascade deletes during conflict resolution. That will save you some code in the future.
Letting aside relationships and validation, ICCD has the same problems of document and key-value sync, just at a different granularity.