2 trumpets, and 2 trombones
This piece is similar to “Largo for strings and piano”, and “Largo and Scherzo for violin, viola and piano.”
In fact, this is the original, on which the others were expanded.
While at quarter note = 80, Largo may seem not the appropriate tempo marking, but I think it is the right feel.
Some general dynamics are written in, but each player should adjust each phrase to balance with the others, according to whether it is an accompanying phrase, or melody, rising or falling.