Was a pretty weak trick. Although maybe the ultimate goal was to get the son? But he could have done a way better job of killing the mom and daughters
I think it was pretty obvious the plan was to get the son. Everyone's focus was on the wife and girls.
Also, she was a terrified woman with her two daughters in a small cabin with a grenade. If she was fricking high kicking boards out of windows she probably would have lost her grip and her daughters die.
All the boards were on the inside of the cabin, making them damn near impossible for a 120 pound woman to bust out.
Also she is pregnant, you're all expecting way too much out of her.