skinshifters usually eat giants, especially in werewolf form, due to sheer numbers as you suspected. however giants with auras, such as Niefel Giants and their cold aura, should do fairly well with a standard E9N9 bless as long as you put up a decent number of them. the blessing gives them plenty of regeneration power and reinvigoration, the aura causes fatigue to the skinshifters, so as long as you can survive a few rounds of attacks from the skinshifters, shouldn't be too hard as long as you have enough to form a massive giant line, to not let the skinshifters completely surround your giants. after 2-3 rounds most of the skinshifters would be frozen from the cold aura, than it's easy picking
but keep in mind that battle magic can change the odds, Fog Warriors, Mass Flight, Warriors of Niefelheim, etc would turn the tide in the skinshifter's favor, likewise you can bring battle magic of your own, say Mass Regeneration, Army of Gold, Weapons of Sharpness, etc. however once Warriors of Niefelheim(or its lesser variants) comes in play cold aura will stop working, which will make it a lot harder. that would be the time for alternative methods such as those Baalz mentioned