I found some approach by drawing a graph of the spies from the lowest number (E = 1) to the highest (A = 4).
So at first we should talk about E. As it comes from the question E have worked with only 1 other spy. So lets see if he's lying or not. If E is lying then he should have never worked with any other spies so then A is also have worked with 3 others ...
We can summarize this information in a graph, where the vertices are the 5 spies, and two spies are connected if they have worked together. Each spy's assertion is then a claim about the degree of the associated vertex.
Are any of the spies liars?
Have B and C worked together?