I agree that it could be either mites or fungal; fungal typically starts out on the face, yet scabs can be attributed to either condition.
I would recommend letting the vet have a thorough check of your piggies as soon as possible. If mites, the vet should prescribe a series of ivermectin treatments, 2-3 doses, each dose 7-14 days apart - preferably injected or orally, not topically (spot on/on the skin) given the skin has broken and scabbed in places.
If fungal, treatment with an anti-fungal shampoo e.g. Malaseb or Nizoral, would be recommended - at least one bath weekly for 3 weeks.