I have not as good experience with network. My pictures are on a NAS server (qnap 509), jpg and raw files (cr2). The catalog is local.
When activating the writing of xmp, the only xmp that are written are from cr2 files. All modification made on jpg files are directly written in the file itself. This is a very strange behaviour. Looking far inside the forum and internet, I have found nothing about this.
Start a new thread if you have an ongoing question is my best suggestion, but sidecar files are created ONLY for RAW files. Others are stored in the image file directly when you tell LR to write out to files.
In Windows (I recommend using a gigabit switch and network cards):
Map your drive from the server to your workstations. Let's say the M: drive is \\servername\sharename
Create a Windows batch file using notpad. In a blank notpad type the following: subst L: \\servername\sharename
Give the batch file a name such as lrmap.bat and save it in a convenient place (desktop or server share.)
Make sure you are not using the L drive. Now run the batch file by clicking it. You will now see your server drive listed as disconnected. Double click it then browse to your catalog (db) file. The catalog will now open in LR. Check your folders and map them through the M drive if necessary or through the L drive if you like that better. Do this on all computers.
You can only work on a catalog from one computer at a time, but if you seperate projects into multiple catalogs you can have people working on different jobs at the same time. Works great for me.