Printing Serial Readings for 2+ Parallax Ping Sensors
Your problem is in how you are working with the two sensors. At the moment you are triggering both sensors together then waiting for the first one to echo back. Only when that has responded do you then wait for the second one to echo back, and that echo has been and gone already.

Imagine you have two tennis balls. You throw them both at different walls at the same time, then attempt to catch them both. While you are catching the first ball the second one bounces off the back of your head and rolls under the table. That's what's happening with your echos.

So instead you need to treat both sensors completely separately. Trigger the first, then get the response. Then trigger the second and get the response.