part of the answer
I've been searching around for the same thing and i just found out what i was doing to create the issue. I normally go control panel > folder options > view tab and then uncheck "Use Sharing Wizard (Recommended)". If you turn that option back on, you are given the option that everyone is talking about. (the "share with" and then the 4 options of nobody, homegroup(read), homegroup(read/write), and specific people)
It seems that you can only share out the library on homegroup if you have "Use Sharing Wizard (Recommended)" checked.
If you right click on the library and you select properties you will see an "Attributes" section. The "Shared" option is grayed out no matter if you have "Use Sharing Wizard...