Miketz: Was Reuven a "foolish oldest son"?

Why does Reuven offer for Yaakov to sacrifice his two sons if something happens to Binyamin - especialy when Reuven has four sons, not two? How is his statement connected to the Yehuda and Tamar story? Is Reuven trying to implicate Yehuda for his role in the selling of Yosef?

And what lessons is the Torah teaching us about the role of the firstborn?