Here's a demo mission
Since we're working with players I used tasks rather than waypoints until the end when AI leads the assault on the barn.
Basically every trigger adds a new task as you do the steps of the mission. First killing the crew, then stealing the car, then reaching Novy Sobor, then joining your group and finally clearing the barn. Sometimes the destination is a marker other times it's an object.
The join a group is simple. I show both joining a group as a member and later becomming the leader. To join a group it's:
[player] joinSilent reconGroup;
Where reconGroup is the name of a group.
To become leader at the end of the mission it's:
reconGroup selectLeader player;
For making the units attack I left the group as AI and gave them Seek and Destroy waypoints. In this case I had a LAV-25 so abandoning the vehicle, your main force projection tool, would be unwise, but i did send it off on it's own to attack. Synched GET OUT for the ground troops and TRANSPORT UNLOAD for the vehicle did the 'everyone out' trick. To abandon you'd just use a GET OUT waypoint.
Coding, don't need forEach with commandGetOut this works:
commandGetOut units groupName;