bass
Timbre
Typically, a group of three instruments or voices is called a trio or a triad. In some rare, informal atmospheres, they are also called tritets, but this almost never happens in a classroom or professional setting.
A piece of music for eight voices or eight instruments would be called an octet. Some noted octets have been written by Beethoven, Mendelssohn, Schubert, Stravinsky, and Steve Reich.
The treble clef or the G clef they are both the same thing
No instruments are used in a Cappella, only your voices.
no
They can be both high and low pitch. There are brass instruments that are considered "high voices" like trumpets, there are brass instruments that are considered "middle voices" like french horns, and then there are brass instruments that are considered "low voices" like trombones, euphoniums, and tubas. All brass instruments have a pretty large range of pitches they can play depending on how good the player is, so the pitches can greatly vary.
song
Octet
it is the melody or succsesion of tones for one of the voices or instruments
timbre
The lowest part in early polyphony is called the tenor voice. It provided the foundation and support for the higher voices in the musical texture, typically sung by male singers. The tenor voice often carried the cantus firmus or melody.