There seems to be two factors to the Law of Magic regarding murder - action, and intent. You have to kill someone directly with magic, and intend to do so. It's a little fuzzy - Butcher describes it like this:
“I meant to shoot him in the leg and wound him, not hit the femoral artery and kill him, so I should not be considered guilty of murder,” is not something that stands up in a court of law /or/ in any serious moral or ethical evaluation. You had the weapon. You knew it was potentially lethal, even if you did attempt to use it in a less than fully lethal fashion. (Or if you DIDN’T know that, you were a freaking idiot playing with people’s lives, something really no less excuseable.) But you chose to employ the weapon anyway. The consequences of those actions are /yours/, your doing, regardless of how innocent your intentions may have been.
Similarly, if you meant to drill that ^@#%er through the eyes, if you had every intention of murdering him outright, but you shot him in the hand and he survived with minor injuries, again the consequences overshadow your intentions. You might have made a stupid or morally queestionable choice, but it isn’t like anyone died or anything. He’s fine (at least in the long term), you’re fine, and there are fewer repercussions–regardless of your hideous intentions. (WoJ)
We have many examples of wizards killing people with the aid of magic, without it counting as a First Law violation. For example, when the White Council killed Kemmler, they magic to help, but not to actually do it:
Technically, they didn’t actually kill him with magic. They rendered him helpless with magic and then found other ways to execute him. (Swords are the usual. For Kemmler, they also used guns, axes, shovels, ropes, a flamethrower, and a number of other extremes.) It’s a semantic difference, in some ways, but an important technical distinction in others. (WoJ)
In this case, the 'technical' distinction seems to apply in the case of the First Law. Magic that sets someone up to be killed isn't a violation of the First Law. The wizards casting the curse are not directly committing murder. Indeed, technically, it may not have caused anyone to die at all (though it did.) They just made them more noticeable. It was the decision of various other supernatural entities to kill anyone.
The Fourth and Fifth Laws ban the violation of someone's mind and enthrallment. This also doesn't apply: nobody's mind is being affected, and nobody is being in thralled. The wizards just threw the magical equivalent of neon paint on Talbot and his descendants.