1st make sure all the waypoints are numbered correctly in sequential order (wp0, wp1, wp2 etc).
To make them follow the waypoint first make the head to the WP then
To make them patrol up and down the waypoint
Also remember to set their awareness levels or their AI will make them break off the waypoint if they detect the enemy.
Set them to higher awareness when you or friendlies hit an area trigger or other variable.