It's great to hear that your dad also cares for your piggy. It is important to understand, and to explain to your dad, that as guinea pigs are prey animals they often hide their illness as long as they can- and when they show signs they are usually quite far along in their illness. This is why it is important to be able to recognise signs of illness, like you have done, and act quick with vet attention. I am not a vet, so I cannot give the best advice, but your guinea pig looks quite poorly. I think you need to see a vet as soon as possible - his eyes look quite sore and I am sure that you do not want your guinea pig to be in pain or suffering.