You mean the Dragon Slayers at the Dragon Cliff Castle in Orobas Fjords?
O yes, they're strong and dangerous, but in fact, even at nightmare diff., it wasn't that difficult for me. My Summon Ghost and Creature (with Rush Attack/Fatality L10) are a great help !
I remember I used Firewall and Stun Arrows and further on I think Explosive Arrows too. All that, while jumping and rolling to evade some attacks ...