If you do not kill them within a very short time, you will die. They are fast, they attack in pairs, and they will try to flank you if they can, so you can't block their attacks. I modified the assassin wilderness encounter, so that Dark Brotherhood assassins now start out invisible, use poisoned blades, and can shoot arrows at you from a distance.

Tired of lame assassins that suck at hiding and try to kill you alone? Play Better Assassins! They come out of nowhere, work together, and kill fast.