ITunes - portion of music library disappears

The essential problem is about 80% of my +/- 2000 song ITunes music library spontaneously disappeared. Some background. The original single library was set up on one computer with three accounts, mine and my two children, and three IPods about 6-7 years ago. And then last week I logged on to purchase songs, the library had gone from about 2000 songs to 300 which are mostly mine, and I got a warning that my account was disconnected from the library. It prompted me to erase and sync my IPod and create a new library from the playlist on my IPod. I did so, probably a mistake. I’m currently trying to get support online via Apple Express Lane using email. However, it’s slow and not very helpful at this point. Also, for the last several years my children got Macs and have Home Shared off all or most of their music. (I’m a PC person so I’m not sure what this means for the architecture of the library.) So I’m wondering if this is a non-problem given the library exists but been mysteriously truncated into three different libraries on three different machines.
Thanks, RB