I think you will have trouble accessing inside a package while the backup is in progress, as the files have not been finalized or written out yet, the files are still open and being modified, and hence restricted access, and many are likely temporary files not the actual files that you want.
Here is what I see in my backups and these folders can be browsed like normal in the Finder (but not the inProgress item). It looks like you are trying access a backup that has not completed yet. I think you have to let it complete before you can access it. Once it completes, it has a folder with a date/time stamp and you can look at the backed up files as if you are in the Finder. A better way to access the files is through the Time Machine browser itself, but you can also use the Finder.

