This and the next one are really easy in certain spots
Chapter 3 - A New World sees you riding a car through a Nazi checkpoint, and leaving it several times to clear the way, on the second stop, you'll go up a few steps where a door will open, and the old dear in the car will gun down the Nazi opening it, BJ will say something like "Hm. Good Aim for an Old Dame" and you'll know you've found the spot i'm refering to, and it's litereally a few seconds past a game checkpoint
if you're on the easiest difficulty, just stand in the doorway, looking at the pillar dead ahead of you, slghtly left of some boxes, 4 Nazi's will enter the room, and the last one ALWAYS stands infront of this pillar and throws a grenade, aim at his legs and as soon as he pulls the pin out with his mouth, gun him down, he'll drop the grenade and BOOM! indirect kills, you can rinse and repeat this by restarting checkpoints to get the 5 kills you need to complete this perk, to unlock:
but i recommend working on the next one straight away with the same guy, instead look in the door and back away as far as you can in a straight line so your back is against the railings but still looking in the door, and aim above the grenade throwing Nazi's head a little, let him throw the grenade which will land where you're stood and hit X to throw it back, i got 3 kills with that on my first got, needing only 5, it can be done with one or two reloaded checkpoints to unlock:
hope this helps anyone stuck with these two perks