Characters lie to each other and force others into lies, and Lehman lies to the entire nation about the ultimately self-destructive financial machinations that are helping poor immigrants, among others, buy homes — a symbol at the heart of the golden promise that is America. At once critical and hopeful, “Behold the Dreamers’’ traces the political and economic systems that push individuals toward dishonesty, while also acknowledging the bad and affirming the good in their complicated personal choices.