how to intercept / ambush from map

[Headshot]

Ok this may seem like a simple set of questions but here goes...

I am not an enemy of anyone as of yet. I have the mission ( gov ) to intercept Tanya's people before they get to olvega and talk with the rebels there. I can spot them on the road and can click on them with what appears to be an intercept icon (the four way arrow). However when I enter the random map space they never enter the map and just pass me by no matter if I wait in tactic mode or strategic mode. What do I have to do?

Do I have to be an enemy already to intercept them?
Will I become an enemy to Tanya if and when I do intercept them?
Also the Government forces already came into Olvega and killed all the rebels including the main guy and his Lwt.
Can I just wait in the town for them to show up since there is no one there for them to talk with? And if so will it fail the mission since they want me to intercept them "Before" they can speak with the other rebels?

I hope for a quick responce .. and thanks

Headshot
If you shoot them in the head they dont often get back up.