A collection.
A person who watches movies might be referred to as a viewer. Also I have heard people call them a movie buff, which means they know a lot of stuff about movies.
Heart players, or gits, or a lot of other rude words. People shouldn't do that, unless you want to get back together too.
two people singing together is a duet
medow They grow together in a meadow. They are put together in a bouquet.
fainters? I guess
Choir
Quartet
A duet.
Horses are just called "horses" unless they are in a group together. When horses get in a group together, they are then called a "herd".
gatherings or gathering
i think it's different for a lot of people, but I call them fireflies :)