B.J. Penn's Mixed Martial Arts: The Book of Knowledge is the perfect present for the Muscle Sharks on your list. Not only is it a very good MMA technique book from one of the best fighters in the sport, its also an invaluable insight into B.J. Penn's approach to MMA and his offensive skill set.
Bj's book is made up of techniques that work for him and would be usable by most people. There are no kicking techniques and no leglocks. What is shown are basic techniques, which if done properly, are always dangerous. Nothing fancy, just master the basics and shove them down your opponent's throat until you beat him.
The glaring absence of kicks from the offensive section of the book really jumped out at me. It's clear that B.J. has focused his style on what works for him and ignored the rest. Too bad for Sherk that he doesn't have any kicking game of his own to take advantage of that with. Sherk's peek-a-boo boxing style also plays into B.J.'s hands as it leads right into the clinch game where B.J. is the master.
Regardless, this is a really useful book -- and I don't even train. The techniques are clearly explained and the philosophy behind B.J.'s fighting style really comes through -- ABC -- Always Be Combining -- B.J. doesn't just grapple and then switch into striking mode, instead moves like "Whizzer into Punch" show you how to use a wrestling technique to set up a nasty punch. And "Half stack pass sequence" features multiple elbow strikes and punches to set up a guard pass.