What happens to MY music if I join a new Family Sharing account My wife already has an iTunes account with her own music library.  She also wants access to my music library.  If I set up Family Sharing and invite her, will she lose her music or will the iPhone display both music from her personal account library AND my account library?  Thanks!
Family Sharing allows all members to access Apps, Books, Tunes etc purchased by all members [though not the 'data content' of any App, so for instance each member's level on Angry Birds, or whatever would not cross-pollinate]. It will also add a shared calendar for which usage is optional.  

It doesn't share anything else. It also doesn't delete anything, only adds.

If your iTunes Library contains CD rips or music not purchased directly via your iTunes account, that would not be available to other family members, you would have to copy it to their Mac/PC/iTunes manually.