They are obviously blood reavers with Garrek having the customary severed head trophy of Khornate champions everywhere. My personal favourite is Blooded Saek with the big double handed axe.
The thought process for my conversions is normally dictated by what bits I can lay my hands on for inspiration! I am very lucky to have access to my local community bits box where I can normally be found rummaging through looking for weapons and armour to adorn my various ork hordes.
My initial forages discovered the end of a bloodthirster whip but not much else (sadly), but it did give me a bit of inspiration; so not a total loss! Browsing my local hobby group (facebook) I noticed a friend who was converting his reavers too, and was willing to split some spare bloodbound bits he had (result!).
Karsus the Chained, was a bit more ambitious then a hand swap. After much trial and error, I finally managed to get the chain glued to simulate him almost throwing (or whipping) the hammer chain forward.
Targor, was the simplest of the 5, I simply swapped the axe hand with a weapon more befitting the other weapons within the group.