I'm sorry to hear about what happened with your guinea pigs. It must be a very stressful and upsetting situation for you.
It's important to first separate the guinea pigs to prevent any further harm from occurring. You should keep the injured guinea pig in a clean and quiet area to allow them to rest and recover.
Regarding veterinary care, I would strongly recommend taking the injured guinea pig to a veterinarian as soon as possible. The vet may be able to prescribe antibiotics and pain medication to prevent infection and manage pain. The vet can also determine if the eye can be saved or if it needs to be removed. Depending on the extent of the injury, surgery may not be necessary. It's worth consulting with the vet to discuss the best course of action for your situation.
In terms of the cost of veterinary care, you can consider reaching out to local animal rescue organizations or charities that may be able to assist with the costs. Some veterinarians may also offer payment plans or financial assistance programs. It's worth asking about these options when you call to make the appointment.
As for surrendering the guinea pigs to a shelter, that is ultimately your decision to make. However, please keep in mind that guinea pigs may have a harder time finding new homes compared to other pets. It's important to consider their well-being and quality of life in any decision you make.
Lastly, I want to remind you that accidents can happen, and it's not your fault. You clearly care about your pets and their well-being, and that's commendable. Please don't be too hard on yourself.