Guinea pigs are not likely to eat their stillborn babies. They don't have the same instinct as some other animals to dispose of their young in this way.
You will need to dispose of the stillborn babies yourself. This can be a difficult task, but it is the responsible thing to do. You can bury them in your garden or take them to a veterinarian to dispose of them properly.
It's important to remember that guinea pigs are very sensitive animals. If you are experiencing this situation, it's best to consult with your veterinarian for advice and support. They can help you understand the reasons behind the stillbirth and how to best care for your grieving mother guinea pig.