I just got the platinum on this after struggling through Crushing. I found it seriously tricky because I'm really not such a great gamer, but I loved every minute of it.
Descendants - blindfire and run - no deaths on crushing here
Final battle - jump back over crate and shoot from cover until you need more ammo. SAS is good here.
By the descendats, I assume you mean the mutated Spaniards? And yes, I know what you mean, I blindfired on Hard difficulty and didn't die once.