In Chapter 4 your whole team (five people for the first time in the game) starts out in the snow. You get attacked by 6 enemies right away. Here you can grind out any skill/kill related achievements. When all the enemies or your team died LOAD the checkpoint. All your progress is saved between reloads. Tactical pause is pressing
. The time stops and you can freely assign 3 actions to every character. Pressing tactical pause again executes it. The command has to finish the enemy so simply targeting them usually doesn't count. The easiest way - for me to ensure I got the kill - was the grenade of Glas. As soon as the checkpoint starts duck
behind the rock with him, pick the grenade and aim to the center of the enemies. Your teammates start wearing the enemies down on their own. When one or more has less than 30% health left pause the game and pull
. Unpause and the greande will kill 1-3 enemies. Reload.
I'm not sure if your progress is saved if you quit the game before you reach another checkpoint. So grind all these kill related achievements in one go.