I've never heard of swollen heads as a symptom of blackhead, and the area you are describing is the sinus. Depending on when you plan to process them, you can give them some antibiotics if you want. I would recommend Tylan injections. If they appear to be getting better, just watch them. What you are seeing is likely a virus, and personally, I wouldn't hesitate to eat the meat even now, I just wouldn't eat the head
If I recall, even birds with AI are safe to eat as long as they are cooked properly. And there are many strains of AI, some are low pathogen and others are high pathogen. That being said, I know that in our state (North Dakota), if they test your birds for AI and they test positive, they'll be back to find out what strain it is and if it's high or low pathogen. Either way, it's very likely that they will destroy all of your birds. I was really sweating when they tested mine since I have had a few with swollen sinus over the past 10 or so years... I was really relieved that they tested clean.