2018 has the new folder structure so 2017 won't find the styles etc..
you would need to install 2017 in another folder but point it to the RealTracks\Drums folder in the 2018 folder.

There are some other files you can copy from 2018 to the 2017 folder so you have all the 2018 Styles, RealTracks and RealDrums, just let me know if you are keen to do this and I will post some more info.