Hello! Welcome to BYC.
From my understanding, you will need to remove all of the pus. You can trying putting a drawing salve, like Prid, on the wound and give it 2-3 days then try removing the pus again. It may take a few tries of treating (using the salve to soften the wound and draw the infection out), wrapping, waiting 2-3 days, checking, and so on... I have also seen Dawn Dish Soap recommended to soften and dissolve the "bumble".
Why breed of chickens do you have and how high are your roosts. Also what type of litter is in the coop and how deep? Do you have pics of bumblefoot in question?
If you have heavy breeds and the roosts are too high, they can get bumble foot from jumping off the roost and landing too hard. This can result in small wounds in the feet that then become infected. I'm guessing this might be the case since you have so many birds with it at once.
Most bumblefoot is cause by a staph infection which is why it is important to remove the whole kernel - this is also why it is important to wear gloves when treating as it is possible for humans to contract staph infection from it.
This is a good article on non-surgical treatment:
https://www.tillysnest.com/2015/12/non-surgical-bumblefoot-treatment-html/
And here are a couple of good videos on treating bumblefoot :