The term "collective right", as generally used, refers to "rights" of the people as a whole or, more typically, the "rights" of 50%+1. The freedom of assembly is definitely not in that sense a collective right. If two people want to assemble they have the right even if the "collective will" of everyone else is that they be forbidden.
I agree. Solo FReeps are protected by the Constitution, of course.
The reference to "of the people" in the rights to peaceably assemble and petition the government is simply a recognition that people can get together in large groups for these purposes. Normally, though not always, demonstrations and petitions involve a group.