And, as MacFamily tree stores the databases and backups made from within that app in a subfolder of ~/Library/Containers your data and backups are backed up by TimeMachine unless you exclude that folder tree. I use their sync service, CloudTree to sync to other machines. Synced files are not where the data is stored, nor a backup. See the MacFamily Tree Menu: Settings → Tab: Databases to where your stuff is locally stored.
As the MacFamily Tree database is really only readable by the app, IMHO I don’t think you should be indexing these files into DEVONthink as I can’t think of any purpose.