Hallo,
if I make a remix from other peoples materials, can I/should I include the parts ? They are not strictly speaking by me, they are reworkings of other peoples sounds, and the site says ” samples must be your own work”

If you are using other peoples sounds in your remix, then the sounds must be licensed with the appropriate cc license. Also you must give attribution to the artist.

By using ccMixter artist source material it makes it easy for you to give credit and track samples in the remix history section of your page. I hope this helps!