Please read the whole OP. The solution is listed there.
I saw this post of yours but my unit is not rooted so i don't know if i still have to follow below or not.
And i don't know how to backup the device in recovery but i downloaded the second third and i have the fourth one.
My suggestion would be to:
1) Backup your device in recovery.
2) Install a backup launcher(like Nova Launcher) from the Play Store.
3) Download "System App Remover (ROOT)" from the Play Store and completely uninstall your current TouchWiz.
4) Try installing the TWS8.apk. (Use the "APK Manager" in "System App Remover (ROOT) to install it if it still won't install on it's own.)
Note: This all assumes you're rooted of course.
If it still doesn't work after that then, then either your variant of the Note 5(if running stock) or perhaps even whatever rom you're running may have some unusual configuration that renders it incompatible.