No, termites are wood boring insects.
Yes, they are. They have protozoa in their stomachs do help digest the wood.
they break down large matter made up of celluose to small particles
They don't decompose the wood-they can digest cellulose; meaning they eat it, literally.
Yes, a termite is considered a decomposer as it eats wood. their teeth must be very sharp If it gets it's teeth stuck into a Beethoven symphony, then yes it's definitely a decomposer!