What Instruments Have The Same Timbre (If Any)

Horn

Oboe

PIccolo

violin

viola

cello

clarinet

bassoon

trumpet

trombone

tuba

What do you mean? Why do you ask, how would you describe timbre?

The question in the topic title abounds in vagueness, and the post itself does not contain a question, but a mere list of instruments. The question of the title seems to be limited to these instruments, although this is nowhere made explicite. Why only these instruments?

Why? What? Where? Etc...

As Phil does, he groups by family. And even then further distinction could be made: put the reeds (oboe, cor angais and bassoon) together. In the brass the trumpet and trombone are somewhat more bright. As opposed to the Tuba, which when played softly can sound like a low 5th horn. But here the timbre depends on the dynamic of the instrument.

Hence my first question. What do you mean?

Yeah, this is a bit of a silly question. All the instruments on your list (arguably all instruments, full stop) have a different timbre. There are some that can be used as acceptable substitutions (xylophone for a string pizz., Eb clarinet for high flute or trumpet) and a list of these are suggested in Blatter's Instrumentation and Orchestration. But the reason why the orchestra is made up of so many different instruments is precisely because they offer so many different timbres. The ensemble which comes closest to homogenous tone is the choir, but even then there is variation between voice types.

Let's not forget each performer has their own timbre too! For example, one french horn's timbre can sound very different from another french horn's timbre. Each instrument, each player, each concert hall (or location) has a different timbre - there are many variables. Just thought I'd like to throw that in too! :-)