The Unmade are a mysterious group of spren. While they are traditionally depicted as personifications of destruction, they are also shown to be individuals. Nevertheless, they have been confirmed to be Splinters of Odium. Odium splintered himself and created the Unmade to be his influence on Roshar. It is through the Unmade that Odium may be able to influence people in how they think or act.
The only confirmed member of this group is Yelig-nar, or Blightwind. He was referenced in one of Dalinar's visions, when he met with Nohadon. (Yelig-nar had broken into Nohadon's chancery and slaughtered all of Nohadon's wordsmen.) Another most likely member is Moelach, who is (in some way) relative to the Death Rattles which augment The Diagram of Taravangian's devise. In addition, Nergaoul may be an Unmade connected to The Thrill.
In Words of Radiance: Chapter 45, upon learning of an animal that speaks, young Shallan declares, "A Voidbringer!" "You'll bring the eyes of the Unmade upon us." The merchant to whom she is speaking responds, "These things live all over Shinovar, young lady. If their speech drew the Unmade, the entire country would be cursed!"
(It seems young Shallan bore some misconception about the Unmade.)
Q. Are the Unmade and the Stormfather the same "class" of being?
A. Technically no, but they are on a similar level. It is a good analogy.