What is the name of these 2 sci fi short stories?

i remember in 7/8th grade we read a sci fi short story of humans going crazy, and two aliens watching them in the dark. the story took place in a suburban neighborhood and everyone turned against each other, thinking the others were aliens. if my memory serves me right the story ended with the aliens making a comment about the humans....... also, another story came to mind. what is the short story about a human colony on mars. i believe there is a food shortage and they need to build a space ship.