Thinking for a bit, Derek comes to a conclusion
"We don't know his speed, but just looking at him I can tell he's, capable. He might be too quick for an ambush, but, ah, damn. The only way I can see this happening is if Mia were to come in with Castella as a supporter, and after the initial surprise, before he can hold any of you as a hostage, Eliana brings attention to herself by taking aim and firing, all the while I'm next to Isaac. As we try to not bring attention to ourselves, I'll charge the spell, him being there to protect me, and again, all of you try to get his attention equally. The priority is for me to not be disturbed. Does this seem reasonable?"