you have 2 options that come to mind..
1)
create a common folder on your nas for your playlists..then point Rpi1 and Rpi2 to that folder on your Nas for playlists..
or) put playlists on Rpi1 and point Rpi2 or more to the playlist folder of Rpi1..
you ll have to use advancedsettings.xml for this
Code
<advancedsettings>
<system>
<playlistspath>smb://rpi1_ip_address/storage/.kodi/userdata/playlists</playlistspath>
</system>
</advancedsettings>
option 2...mount playlist folder from your nas to rpi1 & 2