Walk close towards the couple and overhear their conversation, then follow Tess through the main street. If you bump into one of the security guards, they’ll push Joel down on the street; do it a second time, they’ll kill him. You can see what happens with infected people at the corner of the street; needless to say, that’s not what you want.
Speak with the couple on the right side of the street to trigger an optional conversation. If you move closer to the security guards in the armored vehicle you can overhear their conversation; the same applies to the two guys standing at the corner of the building around the corner. When you’re ready, follow Tess to the gate, then head inside the building she’s headed towards. Move to the back and help Tess move a cabinet out of the way.