The contention for any article should typically be in the introduction. It is the most strongly expressed view that you can gather. Basically, ask yourself, "what is the writer saying?" The writer should be attempting to persuade you about something. What is that something?
It's like when you have an argument with a parent or friend. You say what you want, and then you go on to justify it.
Also, a news article should not have a contention. It is the attempt of a journalist to give a broad overview of an event. Rather, editorials or opinion pieces would have a contention.
As for finding the arguments for the writer's opinion. I don't believe this is what you should be looking for in a language analysis. You should be looking for the persuasive devices that propel these arguments forward. How does the writer get his point of view across? In some instances, it is the complexity of the argument that plays a huge role in convincing the reader. In this instance you would need to identify the argument, but this shouldn't be an issue, as the argument would be strongly asserted. Try and understand where the writer is coming from. Put yourself in his shoes and see what he is trying to say.
Did you mean two writers for the one article or one writer per article?