Welcome to the forum
The pictures aren’t clear enough to see but I think you are referring to a patch around the eye in the first picture. I can’t really see much in pictures 2 and 3.
If it is the patch around the eye then it could be ringworm.
Are they new piggies?
Best thing is to do nothing other than ensure hygiene.
Don’t be tempted to put any treatments on then as you wipe the scene and make it hard for a vet to diagnose accurately. There is nothing you can do until they have seen a vet. If it is the eye you are referring to, then please exercise strict hygiene in case it is ringworm. Ringworm spreads to humans too so make sure you are washing your hands and clothes you wear when handling the piggies etc, . Ringworm can live in the environment for 18 months or so it is important to ensure you aren’t spreading any spores around to perpetuate any infection.
Disinfect the cage with F10 regularly. Wash fabric bedding hot.
The guide I will link in explains everything fully including the cleaning measures, just in case it is a ringworm diagnosis.
What I can say is that you need to reunite your piggies (on neutral territory). Separating them is not necessary and can harm their bond permanently (separating in medical grounds can cause them to refuse to go back together).
If it is something like ringworm then separating them now serves no purpose other than to cause them stress. All piggies would already been exposed to any contagion, so all need treating making separating futile.
Please ensure all piggies are taken to the vet.
1 What is ringworm and how is it treated?
- Ringworm facts
- Available treatments (UK-US-worldwide available products)
- Your customer rights with new guinea pigs
2 Ringworm hygiene during and at the end of treatment
- When to quarantine
- Recommended disinfectants (UK-US-worldwide available brands)
- Disinfection (plastic/hard surfaces, fabrics, wood/toys)
3 Ringworm hygiene/prevention and treatment...