SPOILER ALERT
There are other ways that have been mentioned on these posts already.

They will take a long time though.
1. Keep putting them on the herbs as you do over and over and over.
2. Let the fire go out and then heal all the sick people.
3. Make Sick Stew, make everyone eat it and them heal them.
(Someone on previous posts mentioned it took them 3 stews)
I hope this helps and thanks to everyone who actually came up with these tips!