Both Grieg and Gurlitt's are of the romantic era (mid to late 1800's), Wanhal's style's classical, so compareable with Haydn and Mozart.
Alone At Sunset is also a romantic piece, and is the only piece you play, of so called 'programmatic music' e.g. something that's written to resemble an actual situation from outside the realm of music itself, whereas the other pieces are abstract works that are meant to be enjoyed for their own sake and not also because of the images they are supposed to trigger in your imagination. It's basically a fantasy piece written around one main theme.
Regarding the Wanhal; The most striking characteristic of the Rondo is that one has two or more contrasting themes that are alternated, a bit like an instrumental version of the chorus and verses of a traditional song (also used widely in pop music by the way), the sonatina is written in different parts with a first part in sonata form (A part, B part with different themes, and a transition back to the A part with an alternate ending to serve as the outro (coda) for the piece. I would have liked to be a bit more specific about the other movement, but I can't find the sheet music on IMSLP, too bad.
The Grieg Waltz is a typical waltz with 3 beats per measure with the emphasis on the second beat giving it the characteristic rhythm pattern one would expect in such a piece. Unfortunately the only link I could find on Youtube doesn't work (the recording refuses to load leaving just a black square where the video is supposed to go.
I do hope someone else can fill in the gaps I unfortunately had to leave here due to me not knowing all of the pieces you are playing. Give it your best, and in your answer, just show, in your own words, that you understand what a Sonatina (a small sonata - just look on Wikipedia for a description of sonata for all info), a Rondo, a Waltz, and this so called 'programmatic music' are.
The best of luck for your exam, just relax and show them what you got, aight
Topic: Music Style