Okay . . . I would not cut anything at this point.
If the bumbles popped on their own, they were blisters. What have they been walking on? Did someone put them in a tub of hot water? That has happened, someone not paying attention had the ducklings in the tub and ran the water and the water got hot and blistered the ducklings.
Were they walking on hot pavement? Or on something very very cold?
Could they have been exposed to something toxic? Like cleanser?
Please upload photo's - at this point I would get some antibiotic cream, not ointment, nothing with painkiller, and three times a day dab a little bit on their feet. Be sure they are on good bedding - I might use old towels for now - something not likely to scratch their feet.