While your deciding, wash them so blood doesn’t attract. They are all in shock so I would put them in a confined area and give them time. Give them electrolytes and probiotics for a gallon or two and then go buy a cheap game camera to see what it is. I raised coons all my life. They do eat what they want and leave a mess. But a coon wouldn’t probably attack so many at once. No holes dug around coop or anything? So sad but if necks are straight and they have flesh wounds, you can go down to feed store and buy penicillin. You will need a 17 gage needle because it is very thick. 1/2 cc for 3 days should do. Keep wounds clean and bring them in until healed. I raise both ducks and geese. I bought geese as guardians for them during the day. We ended up buying a metal building because owls eat then like caviar. Want that crop food for babies which are here now for breeding season.